ripster, welcome and thanks for your continuous contributions to GH community!
Magna224,
'T' means tactile feel.
I think all RT tactile keyboards have membrane switch and rubber dome. I don't know whether individual or sheet.
Some model has rubber dome sheet not individual?
Yes, RT8xxx and RT101 are mechanical. I couldn't find other mechanical models.
Disclosure: I don't own any NMB boards and these info comes from just google search and archinve.org.