You're absolutely right that piano rolls are very hit-and-miss! There are two ways to categorize piano rolls: their resale purpose or by their capture method and technology. For simplicity, I'll try to tackle it from the former.
The four main sale purposes of piano rolls were home listening and private concerts, dance hall accompaniment, pianola performance, and original compositions for pianola.
Home listening ranged in tastes from popular music classical performance, and the more expensive rolls were "reproducing" and featured famous artists like Paderewski, Rachmaninoff, Godowsky, Hoffman, Prokofiev, Busoni, von Sauer, Gershwin, Joplin, Granados, Grieg, Horowitz, Rubinstein, Stravinsky, and countless other who's-who of turn-of-the-century piano. Rolls of this kind were produced in all genres are usually considering the highest quality of piano roll, but getting good results from a piano rolls is its own art form, even with the help of MIDI. Each manufacturer had their own "reproducing" systems for playback or recording: some captured key velocity, but as a general rule all public domain piano rolls get their velocity (equivalent) data from technicians who would manually modify every note on the roll to give it the correct intensity. Some technicians took a lot of time and put a lot of care into refining the piano roll, but others--usually working for smaller companies--did not. This is probably the biggest reason that piano rolls are random, even between the same brand, artist, and year of production. Also, even when companies had better capture of key velocity in playback, technicians would still modify the roll after it was created, so I've found it's wisest to discount the velocity on any piano roll as not being representative of the original performer. Reproducing, when available, was the recording method of choice, even if the soloist wasn't necessarily the selling point of the roll, since reproducing rolls took much less time overall to create, edit, and produce. There are also a number of pianists who gained notoriety that translated into larger careers for being piano roll "recorders" and if you scroll through the entire Ampico catalog, you'll see a lot of names--that while having fallen into obscurity since then--were quite famous because of their piano roll even if they didn't have wider fame, like Victor Wittgenstein (not to be confused with Paul Wittgenstein).
Timing was rarely adjusted on these "reproducing" rolls but that happened occasionally (as shown in the dance rolls below), whereas velocity was changed at least 90% of the time. Home listeners also purchased "arranged" rolls which are either totally synthetic performances for piano that arrange large orchestral works or feature a real performance of a skeletal version of a large work with additional "overdubs" of automated or human recorded performances on top of it. The handful of piano concerto piano rolls that are/were on the market were created with this process: a soloist records the solo piano and keeps adding the orchestra part through multiple overdub runs of the piano roll in subsequent takes, or the solo part is performed and then the orchestra part is punched into the roll by hand.
Dance halls and other venues where pianolas were used as accompaniment for dancing to used piano rolls specifically designed for dance use. Often, the dances were recorded from notable recording artists of classical or popular genre--like the better reproducing rolls, but the timing was "quantized" like it is with midi to keep the dance steps perfectly in-time. A lot of the Joplin or Gershwin rolls were subjected to this, if the company wanted to market it to what are the precursors of modern DJs who operated pianolas at dance halls. This was a common role in multiple venues, much like theatre organists for silent film accompaniment, which has been largely forgotten. While the Regency-era balls of Jane Austen's time were more ostentatious social gatherings, it was typical--whether at the local music hall, someone's barn, a bar, or a living room--to have a pianola and a DJ-of-sorts who spent the majority of their time accompanying dances. The pianola operators would often also act as a dance move "callers" depending on the setting or type of dance. Ironically, the later occupation has survived while the player piano operation aspects are mostly gone. Rolls could also accompany singers and many piano rolls have song lyrics or composer annotations written on them (Danse Macabre by Saint-Saens often has poetry about the musical imagery that follows along with the performance). It can be hard to guess if a piano roll was time-shifted for dance use, unless you carefully explore the MIDI data, but if it a dance form of music from any era, there's a good chance it was modified, even if it is a "reproducing" roll.
The third category of users and uses of piano rolls are the pianola performers. These were typically bar or music hall musicians (who may also have worked with dances like the above) but they specialized in altering the piano roll playback (like a DJ scratching vinyl) or played additional music alongside the piano roll. These rolls were sometimes 65-note rolls (though not always) since the smaller compass of those rolls gave the performer greater flexibility in adding new soprano or bass lines with the extra octave. Performers would "play" the front controls of the player piano to speed up or slow down the performance (much like we humanize MIDI tempo data) and add their own chords, accompaniment, descants, or ornamentation through improvisation. Jazz, ragtime, and other non-classical genres were the typical styles for these rolls, but theoretically any piano roll could be used in this way but most classical-genre arranged rolls or reproducing rolls don't really lend themselves to additions. However, it was common practice by Chopin (long before the pianola) to improvise descants and counterpoints while his students played his music to give them better insight into the structure of his waltzes and other solo pieces; though improvisation in classical music has been reduced to nearly total taboo, around the turn of the century, it was far more acceptable than we're used to. Hardly any of these rolls were reproducing, instead these were usually fixed tempo and--sometimes--fixed velocity rolls with the expectation that the pianola player would add the human touch that was marketed in the reproducing rolls.
The final category (and also the rarest) are original compositions for pianola. From composers like Stravinsky and Hindemith, works were created that explored what was possible do to and with a piano without a performer. Feats that would be physically impossible or dangerous for any soloist could be performed by the machinery of the pianola. Inhumanly fast repetitions, instant multi-octave skips, fifteen-note chords were all markers of these compositions. I confess I'm not terribly partial to much of what I've heard that's composed specifically for pianola: there are limits to the loudness and cacophonous-ness that I can stand. These are quite similar to the arranged rolls in being impractical for a single pianist, but they differ in being original compositions only intended for pianola, not piano reductions or arrangements of existing works.
As I have more time, I will see about doing a write-up on the different companies and their different technologies, since each brand had their own innovations that they added to the mix, which makes the history significantly more complicated...and interesting.
Example of reproducing rolls:
https://www.youtube.com/watch?v=_ldMAcJ0W24
https://www.youtube.com/watch?v=fFc3Xk5bsO0
https://www.youtube.com/watch?v=pRvVlMAjzEI
Example of arranged rolls:
https://www.youtube.com/watch?v=Ssi4HE64Deo
https://www.youtube.com/watch?v=jwHK6k-lto0
https://www.youtube.com/watch?v=5q3iAJHZXDw
Example of "performing" a pianola:
https://www.youtube.com/watch?v=Hz_9CXIIZqw
Example of dance rolls:
https://www.youtube.com/watch?v=DVkeOAAsH5E (this one shows different speeds for singing to it and dancing to it)
Example of composed rolls:
https://www.youtube.com/watch?v=7hum6PgRk6k
Mini-documentaries on piano rolls and systems and more information:
https://www.youtube.com/watch?v=w-XrDw04P2M
https://www.youtube.com/watch?v=i3FTaGwfXPM
Spotify:
https://open.spotify.com/artist/2xHiPcCsm29R12HX4eXd4JPianoteq Studio & Organteq
Casio GP300 & Custom organ console
