See e.g. SirDice's comment (basically no, there aren't different versions of ports):different ports tree for each version
There is and always has been only one ports tree. All versions on all architectures use the same tree. It has always been version controlled, but there never was a relation with the version of the base OS. It was version controlled with CVS, later with subversion, and nowadays it uses git. The current git tree actually contains the entire history.Would I need a different ports tree for each version?