It does discolor over time. The point is that one should be thinking about the impact over centuries and not years. It needs to be used with care and other alternatives need to always be considered.

For a painting or building that has survived for half a millennium we need use methods that will preserve the object for another 500 years.

Too many times I hear people say we will just use Paraloid.

Didn't really know of the different 9(!) versions of it. Thanks for pointing it out.