If I were you BM101 (Chris) I wouldn't worry about it. You aren't the 1st to have missed the point of a post, and you certainly won't be the last - and that includes me, in Spades, doubled!!
But reading back through this whole thread, we don't seem to have got a definitive answer - responses seem to vary from "almost forever" to "yesterday" (paraphrasing somewhat)
Personally I'd really like to know if there is a definitive answer, especially for someone like me who does not use a lot of PVA, and not all that regularly either.
Example: I have a 1 litre bottle of PVA marked "wasserfest" (directly translated that means waterproof, but personally I'd rather regard that as meaning water-resistant (after hardening). That bottle is about 2 years old (max) and is always stored in my warm dry cellar, NEVER outside in the extra hot (right now 35 deg C) or extra cold (could be minus about 15 C).
I used some just this week (repairs to a garden gate) and although stored tightly closed and inside, as above, I found it had the consistency of very thick treacle or honey. No mould or anything, but would not even drop off the gluing brush. I used it anyway, it was quite difficult to spread out, but after overnight drying clamped, it seems fine - joints nice and close, no looseness anywhere.
So my question is, as a not very frequent user, especially not of the water resistant type, what happens when I need it again? can I thin it with water, well stirred in, until it's more or less back to it's normal creamy consistency? Or do I just bin it, bearing in mind that I will MAYBE need it again in a week or so, maybe not for 6 months?
I do appreciate that such stuff is pretty cheap and is a consumable, and not worth risking on an important job.
So perhaps next time, instead of buying a litre I should buy a quarter of that (which works out even more expensive that in multi-litre or gallon sizes). In fact, depending on answers here, perhaps I should change my buying habits altogether (as far as any PVA is concerned) and only go and buy very small quantities as and when I really need it? Up to now I've tended to treat it like "standard size" nuts bolts n washers for example - always some in stock.
I'd be interested in others ideas on this.
TIA