Thanks for sharing your experiments with BZ and expired color paper! The benchmark, SupraII exposure, to my eyes at least, has an unacceptable amount of base fog. It looks like at least 5cc of yellow and a few cc's of red over what should be a clean white. The agfa examples serve to demonstrate just how poorly color papers age (this stuff must be at least 10 years out of date). Most remarkable to me is the last example, expired ultra with BZ. Here you're very close to a base white. The exposure appears a bit heavy and I'm assuming that the color density is suffering a bit because of it. Did you have to print it down in order to get a proper black? But the difference between Ultra with BZ and without is astonishing. I'm surprised that you regard the non-BZ Ultra as having more accurate color than the BZ Ultra as, of the five examples, #4 (non BZ ultra) appears to me to have the worst color of all.
Again, thanks for your hard work and concrete examples - these kind of posts make APUG worthwhile.