That pedal is usually called the 'moderator'. To call it 'sordino' in English is at least a bit misleading, since 'sordino' is just the Italian word for 'damper', and the 'damper pedal' is actually the sustain pedal. Italians call the sustain pedal 'forte' if I am not mistaken, so it is less confusing there. Playing una corda results in a somewhat similar effect, because fewer strings are hit and by a different area of the hammer, which is in my opinion the reason the moderator is not common anymore.
That said, the moderator was a common feature of fortepianos, that's true. Though as far as I know it more often than not was not a 'pedal', or even a knee lever: it had to be operated by hand. Apart from that, history does not seem to be the strongest suit of Mr Margulis anyway, and especially a pianist should in my opinion know anyhow that e.g. the instruction 'sempre pp e senza sordini' as found in the first movement of the Moonlight Sonata does not mean the moderator. The whole technical description is also... misleading, to put it mildly. A moderator usually should not permanently touch the strings, because if it did, this would not just result in a 'softer tone' but rather in a very short tone...
Because the moderator is traditionally not a 'pedal', at least as far as I know, its usage is a decision usually made for the whole piece, not just for a few bars or even single notes. And a quite similar effect can be reached by changing the piano's voicing, e.g. by softening the hammers, which is a feature Pianoteq already offers.
Pianoteq 6 Standard (Steinway D&B, Grotrian, Petrof, Steingraeber, Bechstein, Blüthner, K2, YC5, U4, Kremsegg 1&2, Karsten, Electric, Hohner)
