Did Nixon Erase My Tape?

During my Army days in the early 70s, I bought stereo pieces while I was overseas and had them sent home to wait for me when I got out. One of the pieces was a Teac RTR, and over the next 12-15 years, I made around 50 7" tape mixes, all of them at 7 1/2 IPS. I still have those tapes and have acquired three nice RTRs.....a Teac A-4300SX, a Teac X-1000R, and an Akai GX-636. I was playing a tape today on the X-1000 and when I hit 'reverse' to play the second side, all I got was silence, with an occasional garbled sound every 5 seconds or so. At first, I thought maybe I had erased the second side and never re-recorded back over it, but the back of the box (where you would write in whatever you recorded) showed no changes.So I removed the tape from the right take-up reel, flipped it over so that the B side was now the A side and re-threaded the tape back on the left reel. The recording played beautifully, with no problems, and I'm trying to figure out where the problem lies. The tape was originally recorded on a Teac A-4010SL and I think this is the first time I've played it in at least 20 years. I'm thinking that tracks 2 and 4 just don't line up correctly with the reverse-playback heads on the X-1000, which itself seems goofy to me. Any veteran tape-heads out there that have an opinion, please let me know. The X-1000R has bi-directional recording capability, which the A-4010SL did not.