railwayman3, slide films go lighter (DMAX goes up rapidly) when they get old. It's basically the same as fog in C-41 films; if you printed them with the same exposure than fresh film, the prints would be lighter due to fog in film! In chrome films, reversing is done chemically, but the principle is same; fog makes image lighter. This is because there is more silver in the negative after First Development due to fog. No dye will be formed at the silver sites, leading to weaker DMAX and lighter images.
But well, on the other hand, sometimes the Dmin may also suffer (muddy highlights), so, it's not only Dmax.
If the processing is standard, the best way IMO to start experimenting with expired slide film is to shoot normally. If you can modify the process, pull processing (combined with overexposure to get it right) will reduce fog in first silver negative and thus give better DMAX.
It's still surprising not to have any image at all from a 14 year old film. I get usable results from 10 year old chrome films.