This is the case for new users. Once you get a few more posts under your belt, the forums will allow you to post links. (I fixed up your links for you)
There used to be online reference pages for 3.x, but they’ve been removed. The 4.x reference pages document the minimum version for each function, but they don’t provide any help where the behaviour of an existing function has been extended (e.g. additional enumerants, increased minimum implementation limits, or relaxed constraints).
The only available resources are the specifications, but the structure isn’t convenient if you’re trying to write an application for a particular API revision (as opposed to writing an implementation). Apart from the 3.1 specification, later versions summarise the changes for each revision. The 4.1 specification has sections for each revision from 3.0 to 4.1 inclusive, while the 4.6 specification has sections for each revision from 4.2 to 4.6 inclusive. This should give you a list of cases where information in the online reference pages doesn’t apply to 3.1.