I've always treated salted paper ( with or without gelatin or starch or citrate ) as indefinite -- and I salt paper in large batches. But it does make sense to think about it, because some chemical changes in paper can happen slowly over a long time. A few years ago I was using a kind of paper that needed acidification for making calotypes... and the iodized paper worked okay if it was used within a few weeks, but after a few months of storage it started to fog again. So there was some kind of slow reaction going on.... and that's similar to your question: we usually think iodized paper can be stored indefinitely and with most kinds of paper that seems to be true.
Interesting that you bring this up just now. A few months ago I got worried about exactly this issue, and ran a series of tests. I had some fogging showing up on some of my prints and I couldn't think of anything to explain it except that some of my salted paper had been stored longer before I sensitized and printed it. I was using starch instead of gelatin, but it was the same concern. I ran a long set of tests ( sensitizing some paper every day for a couple weeks, then again > 1 months later ) and eventually discovered that the problem was intermittent contamination of my brush ( it was maddening to try to figure it out... because I had recent fog-free prints made with the same brush... it was the new starch coating I was using that slowly contaminated it over time! )
So, I still think salted paper ( plain or with gelatin or with starch ) can probably be stored indefinitely.
