This will require a very simple answer:

I currently do not see any events on the calendar for La Scala for the time I will be in Milan (September 21-23). This seems strange as it includes a Friday and Saturday. Is it likely they will add something on those dates?

Don't see any reason they would have no events those nights.

It appears from a bit of Googling that there is an invitation only dress rehearsal of La Boheme for the elderly and young people on Sept 22.

It also appears to me from a bit of googling that a Milan business association has rented the theatre for the night of the 23rd to have an awards ceremony.

Can't find anything about the 21st, but it may be that La Boheme is in rehearsals. You might call the theatre directly to inquire if you can attend either the 21 or the 22.

PS, cdispoto,

Don't despair of seeing La Boheme at La Scala so long as your plans to be in Milan aren't also your final days in Italy.

Fast trains in Italy are such that you can visit someplace else in Italy until La Boheme opens and then zip back into Milan for a night to see a performance. You won't be able to get into opening night at La Scala, but you have a shot at anything after that for however long you are here.

It will add extra bucks to be sure, but you can almost always find a way to economize along the way during the rest of your trip and make up for the money someplace else without even noticing.

Hmmm, I wasn't even planning La Boheme, just wanted to see SOMETHING there. But I've seen that La Boheme being there is a pretty big deal so now I'm thinking about it. Thanks for the tip, maybe I will try and squeeze it in from another city. I'll be spending the night of 9/28 in Florence and it's a two-hour train ride to Milan, so that might be possible.

Yes, it would be simple to go from Firenze. Don't forget , too, there are many other opera houses in other cities. Napoli, Venezia, Padova, Bologna (50 mins from Firenze)...