The problem is that there are many possible sets of rules, and there's also the fact that over time a given challenge can be easier to do when a new version arises.
For example, during 1.35 it was not possible to bp edit and make a probe ridiculously small to reach orbit with the slightest possible mass, but on the other hand fairings were immune to drag, and this could be used to optimize a launcher.
Then during 1.4 drag was a big mess, it was disabled by default, but it was possible to re-enable it. But then it was terribly bugged. And there was also the problem that somebody decided for the whole forum that everybody had to play with drag on.
Then version 1.5 fixed all that, but now the heat damage prevents from stacking engines like many of us used to do before.
So honestly in these conditions it's hard to define a "record of all times". I'll take the Komodo for example. It was certainly a record under 1.4. But that launcher wouldn't work in 1.5 because of heat damages generated by stacked engines. On the other side, now that infinite build area is available it's easy to bp edit very large launchers, and it's even easier if you play the modded Steam version that allows you to edit parts in just a few clicks without leaving the game. It became so ridiculous that at some point I made popular a joke that consisted in launching other players' launchers with a super launcher. That's what Mooncrasher meant when he said it was just the contest of who would enter the biggest numbers in the bp file.