Topic: Una Corda?

I recently explained the meaning of the abbreviations U.C. (Una Corda) and T.C. (Tre Corde) when playing a grand piano to one of my pupils.

On the grand pianos I have played the Una Corda pedal results in hitting 2 of the 3 strings for most keys, instead of only 1 as the term suggests.
Maybe someone can tell me more about the history behind the term Una Corda?
But also I was wondering how the Pianoteq technology interprets and models this. Using one or two virtual strings out of three?