Thanks to everyone who made suggestions on this topic.
I did an RC-50 experiment tonight.
2 bar loop of the guide in the RC-50 and looped it in pro tools.
I recorded a 10 minute segment of the guide in the RC-50 without sending midi clock to it
it did the same thing it has always done, won't sync to PT's click. so the theory of the approximate tap tempo is debunked. apparently the RC-50 doesn't care if you use the knob or tap, it's going to mess it up the same amount.
recorded a 10 minute segment of the guide with midi beat clock into the RC-50 from pro tools
the guide was 1600 samples behind pro tools click, so I put a delay on PT's click. it seemed to shift somewhere between 1600 samples an 1400 samples behind PT.
re-recorded the guide for 10 minutes and lined it up to the previously recorded guide. THAT worked perfectly !!!!!!!
SO.... in conclusion, to answer my own question:
The RC-50 has a mind of it's own and if you want to re-record things in later from it, better to just play it in for the duration of the song. OR the RC-50's tempo display is off/slow by about .05 bpm at 120 bpm.