Since the SMPTE stripe is the same and on the same place on the tape every time, any drift is a failure of something to function to spec.
Right...but tape transport is a mechanical function, right....and wow & flutter is there with most decks (even brand spanky new ones to a small degree and who the heck has a brand new deck these days
). So even though the SMPTE is on the tape "in the same place"...if the tape motion is being affected by the mechanics, then the SMPTE is affected too.
I mean....I'm not saying that it will drift out by "seconds", which would only be the case in some of your scenarios with wrong SMPTE formats being used between dumps and whatnot...
...but there could be drift at sample/frame level, you just have to zoom-in at the DAW and look at the tails of your tracks. I mean...just dump the same audio track 4-5 different times, and then look at the tails.
If you just listen to the music, and are say... first dumping your drums, bass and rhythm guitar, then on the next pass your vocals and leads....there are no two identical tracks to compare the samples with, so it will all look in time and sound close enough.
Drop a click track on the tape....then do 4-5 individual dumps of that click track with the tape as master...then compare the clicks in the DAW along all the tracks to their end. There will be drift in the first scenario below:
1. You let the DAW run free with its internal clock, and let that and the deck's mechanics dictate the SMPTE speed consitancy.
2. If you tell the DAW to chase and try to be sample-accurate....it is then forced to adjust its speed and do resampling on the fly to stay in sync with any tape/SMPTE transport fluctuations, which could cause an audio glitch at worst, but at best, the DAW will adjust its speed and do digital resampling to stay accurate to the SMPTE off the tape.
It's up to you decide if you are willing to accept digital resampling-on-the-fly for your audio tracks.
When I went with the MicroLynx setup (partly on your suggestion)...I spent a lot of time researching what others were doing with DAW/tape sync setups.....and 100% of those people who still did serious tape work in their A/V studios said that the absolute best-case scenario to avoid any drift issues was to make the DAW master, otherwise you had either scenario #1 or #2 above.
Also, when following the best-case with DAW as master in any A/V mechanical/analog tape setup, it was strongly suggested to also use a video generator with blackburst, and let the MicroLynx (or whatever sync box you had) lock to it for "house sync".
Within the ML manual there is outlined a SMPTE tape striping process using blackburst as house sync that will let your tape deck run virtually free of any wow & flutter if done as outlined, since the ML will then control the capstan at all times.
You can then run the tape a hundred times and it WILL run the exact same way twice, since the ML will "make up" for any mechanical fluctuations from pass to pass....but otherwise, letting a deck "run free" on its own internal clock will not be 100% stable, excatly the same way on every pass 100% of the time....especially with an older, or worn deck.
Trust me....I tried very hard do stay with the tape deck as master, because I hate the fact that when DAW is master, if you move the DAW playback head the tape deck is constantly jumping to chase it, so if you want to work DAW-only for a few seconds, you have disconnect the tape from the sync setup.
By running tape as master, that's avoided....BUT...then the sample/frame level drift is there or the DAW ends up chasing/resampling your audio on the fly in order to keep it "in sync" for every dump, and neither of those options are as good as letting DAW be the master where you have NO resmapling, and NO mechanical fluctuation issues....dump after dump....even if/as the deck transport and tape physically change/get worn over time.
So that is the 100% rock solid setup.
All that said....I ran with tape as master for a lot of years, and as I said in an earlier post...it was fine for Rock & Roll. There were times when I had to nudge things here and there, and times when it was not enough to matter....but the sampe/frame level drift was there. With my current syn setup I can avoid that and run the DAW as master....I just hit the "All Stop" on the ML and "disconnect" the DAW or tape deck from the sync setup when I want to mess around in the DAW for a bit, and not have the tape deck jumping around chasing the DAW.