Why can I choose different Revit versions in question 4, but not different versions of the other software?
Revit is know to have issues with backward compatibility

Where can  I send feedback?
Please e-mail it to leon.vanberlo@tno.nl

I didn’t get an e-mail with an invitation. What now?
Check your spambox. If that doens’t help ask the initiator to send you the link (he can copy-paste the link from the ‘my protocols’-section).