I haven't experienced any going bad. Towards the end of the bottle, particularly if its been around for a while, it needs thinning or just throwing away but 95% of the bottle is always useable. I live in a small unit with limited space and no tolerance for fumes, so Vallejo are ideal. Alexis, when you say "metal" what do you mean? I do admit, I use Vallejo for aluminium, steel etc but when it comes to brass, copper etc I break my rule and use ALCLAD.
I agree moving the contents to the bottom of the label was a weird move. I guess it was the marketing department in their eternal search for relevance.
Cheers,
Ian