SXM2 vs SXM3 dimensions and pin count

The specs for the various SXM2, SXM3, SXM4, SXM5 connectors seem to be trade secret, or proprietary to the point where you can’t talk about it unless all parties involved in the discussion are members of the PCI-SIG. Otherwise this info should exist somewhere on the internet and it doesn’t. It’s quite frustrating.

As far as I know SXM2 connector is physically incompatible with SXM4 and SXM5. They are different dimensions and pin count. I’m not 100 percent sure but based on guesstimation.

Is SXM2 and SXM3 also not physically compatible?

It would really help to have specs for these things, but it seems impossible.