Identify this shower diverter valve
It is Grohe model 29733





How I found it...

After weeks of searching, I stumbled on a picture of a diverter handle that has the same icons for shower and hand-held positions that my handle has (see the third picture in the original question). Knowing that the handle in that picture was made by Grohe, I started searching Grohe's website and found an almost identical diverter (based on the parts I can see). The only thing that is different is the length of the knurled part of the stem.

Grohe 2-Way Diverter Rough-In Valve Model 29712000



Armed with this knowledge, I used the WayBack Machine to find an older model.