WATCH: SLIDE TO FRAME FIT ON 92 SERIES PISTOLS WITH RED DOT READY SLIDES

Why won't the RDO slide work on my 92A1 frame?

The 92A1 frame is different in the recoil spring area, specifically there is a bushing in the frame and a larger nose/dust cover that impacts that bushing in recoil. The standard slide, like the Elite slide, would damage that bushing in the 92A1 because it would not contact it correctly.