Do alternate python implementation version numbers imply that they provide the same syntax?
Question: for example Jython is at version 2.5.1, does that imply a parallel fidelity to
cpython syntax when it was at version 2.5.1?


Answer: Generally yes, but there's technically nothing stopping alternate
implementations from choosing whatever version numbers they want.

It's also important to note that just because Jython 2.5.1 is intended to
match CPython 2.5.1, doesn't mean that they're going to behave exactly the
same or be entirely compatible -- consider C-based modules, for example, and
facilities for getting at the underlying bytecode.

The lack of any real standards body or formal specification for the Python
language means that there are no clear rules on what constitutes "Python" and
what is "implementation defined".

