Comment 7 for bug 1307532

-a is only the date at which the original version came out, that isn't the date that matters for Ubuntu since, like most distros, we backport security fixes.

-b will show you when the package was built, and that is what is important.

You probably shouldn't attempt to maintain your own openssl, it will be much easier to stay up-to-date with security fixes if you use the one packaged.