I actually had another roll of 400TMY from the same source, expired 11/2004, but in uncompromised foil bag. I just exposed this roll in the same camera, same lens, same shutter, same light meter. Processed it identically to yesterday's version. The neg is being dried as I post this.
Scanning the neg indicates to me that this well sealed but expired 400TMY is also grainy, though not as bad as the one from yesterday. The grain is worse than Delta 3200 at EI 1600 (and it goes without saying worse than HP5 Plus).
10 years old HP5 Plus stock works just fine, so does this mean 400TMY ages faster??