It's a Longshot but maybe the tape is still there. Sure it was bait, but then again... it WAS there. It seems silly to say a tape could have survived all that, but it was in a protective casing. If you find the spot, maybe take a note, put it in a ziplock bag that reads "maybe we can trade? One of mine for yours?" Then set a date to come back and see if it's placed there. But you'd have to follow through on the deal. And not an empty tape. Maybe don't do this at all though lol.

Also, are you sure all those tapes are empty? Have you looked in to the idea of there being spectrogram images within the white noise? You may need to not only digitalize the video but seperate and isolate the audio straight from the tapes. Good luck! I'd be interested to know if you see anyone.