I suspect the tape is the problem here. We have Kodak Durol tapes that reek of acetic acid, so they definitely have an acetate base, yet they do not transmit light.
We also have plenty of cellulose acetate negatives which smell terrible, but they are generally from the 1930s and 40s. If your slides are newer, they are probably on a triacetate base. They will succumb to vinegar syndrome eventually; they just might be too young to exhibit symptoms today.
Cold storage is the best environment for the slides. If they are colour, the dyes will fade much more slowly in cold storage, too.
Acting Archives Manager
City of Vancouver Archives
1150 Chestnut Street,
Vancouver, B.C. V6J 3J9