Yes, they should:
datetime has been declare obsolete and not any more maintained. It is still in the distributions for allowing compilation of older documents without needing to change them.
The new package
datetime2 is different and incompatible with its predecessor, so questions dealing with it should not be confused with those referring to the obsolete version.
In general, if the entity they represent is considered different, then separate tags would be okay. However, never use version-related tags, as versions become outdated and therefore typically useless.
For example, while we do have a texlive2010 tag, it was has been voted as a synonym for texlive, and rightly so. There would be little value in having a tag for each version of TeX Live. In the same way, version-specific tags for packages (or software) would not be very helpful.