Hmmm, I’m hoping this doesn’t take a decade but I have less than 50 tapes.
Is there anything in particular that you suggest I do to help to ensure success other than to monitor the transfers in real time to try to listen for any anomalies? The tapes have barely been played (basically recorded and then played back to transfer to computer (many years ago, originally through analog cable). So far the deck seems to be functioning fine but I realize these are finicky machines and I not need it to work to transfer my masters cleanly to the computer so I’m hopeful.
I would try to make sure the playback machine is reliable, as a mechanical failure usually ruins a section of tape. Great if it's the same machine used for the recording, less chance of a compatibility problem.
You may have no problem at all playing 50 tapes, or any one tape could clog the head. Sometimes, a DAT/DDS cleaning tape can fix it, sometimes you have to manually clean the drum with video head chamois sticks, plus the tape path.
I'd recommend monitoring the transfers with headphones, even if not too loud will focus your attention to anomalies. You might hear obvious digital fuzz errors, or a tiny, momentary buzz. My method was to transfer to a computer DAW program, and if I heard a small problem, I would let it continue but make a marker on the file, and check them all afterwards. I might be able to go back, replay a section several times, and get a clean playback I could splice in. Sometimes, head cleaning would be needed first.
As an absolute last ditch effort, if I could not get a clean digital transfer, a few times I found that an analog playback had more error correction/concealment than a digital transfer, and I would match up and splice in a section of analog playback. A few times, there was no alternative to leaving a section with digital noise and just make a notation.
I assumed these transfers would be the last ever done, so I felt some care was appropriate. With luck, you may have no problems, but the tapes and machines are getting old and could have problems.