From time to time, but not at this precise moment, development has
happened on some "future code branch" of Vim, which was then labeled as
either "alpha" or "beta". Important security-and-stability bug fixes
have been, at such times, backported from the "future" release to the
"current stable" release. Nowadays, however, the only code branch
visibly under development is the current stable branch, namely Vim
7.3.x, and all previous branches are at EOL AFAICT. This means that, as
Gary said, currently each new patchlevel obsoletes all previous ones:
the current version is 7.3.744 released some three hours ago as I'm
typing this message. Like Ben said, any bug found in some earlier
release will still be investigated and, if some already published
patchlevel did not fix it, a fix will be attempted, and, if found and
accepted by Bram, published as a new patchlevel, etc.
Someday an alpha or beta pre-release of 7.4 or 8.0 will probably appear,
and then we will again be in the other, "transition" case described at
the beginning of the previous paragraph, until a new "stable" 7.4 or 8.0
release obsoletes the 7.3.x branch.
Best regards,
Tony.
--
The penalty for laughing in a courtroom is six months in jail; if it
were not for this penalty, the jury would never hear the evidence.
-- H. L. Mencken