Hong Kong teas are usually exposed to more humidity than most other areas, and therefore age "faster" than they would in a drier climate such as Kunming. This isn't a bad thing, per se, but it usually loses a lot of subtle nuances in sacrifice for a smoother, darker tea. The result of this is a characteristic wet storage taste which could be perceived as moldy. Wet cellar floors, old books, a pile of fall leaves, forest floor, etc. I would expect a Hong Kong stored tea from the late 90's to fit your description. The leaves would probably look like a lightly fermented shu.
As far as telling you what steeped leaves of older raw puer should look like, I'm afraid that it is something that kind of comes with experience. I have teas that have been in only my possession since being produced from the same year that look a little different from each other. I'm only talking about teas that are six years old as well. There seem to be many variables that go into what the spent leaves should look like after certain periods of time.
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