SLT Mirrors A33-A77

I was reading the posr regarding the Sony a35 bokeh stripes. One poster comments that the mirror is an updated version of the older mirros A33 i suppose.

My A77 has just been repaired - i took the chance to buy a backup mirror for field exchange. The box the mirror is in indicates A1855640A, P.O.I (service) and SLT A33.

• Is this the incorrect part?

• did the mirror never change?

• did the mirror change (upgrade) and it fits for all SLTs

Cheers
R