Mightn't this be just a difference of radically different times required for the film developer?(posted 9200 days ago)From what you've described, it's definitely the developer. Once upon a time I got my chemicals swapped around in the process, and I used hypo clear before the fixer. Well, I inspect my negatives immediately after fixing them. When I pulled the roll out of the tank, you can imagine my suprise when I saw the negative on an opaque background. I then realised my error, ran the negatives through the fixer, and all was well.
Other than running a test strip, no, you can't tell when a batch of developer might be bad. But you don't need much for a test strip. Just expose a roll of 35mm at something, then wind the film almost all the way into the canister. Using a dark bag, cut off a square or so and leave a bit on the canister so you can easily grab some more from it. Develop the square, and there you have your test strip.