po-devs/pokemon-online — pull request #1172 by Fuzzysqurl (2014-06-19 03:36:49+00:00)
Title: GSC Boost fix

Source: http://www.upokecenter.com/content/pokemon-gold-version-silver-version-and-crystal-version-timing-notes
"2. If the attack has an additional effect such as a stat stage modification, poisoning, or burning, the probability of the effect happening is now determined. If a random integer from 0 through 255 is less than the attack’s additional effect chance, the additional effect will occur. For instance, for Blizzard, there is a 51/256 chance the opposing Pokémon will become frozen. ``The additional effect won’t occur if the opposing Pokémon faints because of damage, even if the attack is Ancientpower, Metal Claw, or Steel Wing.``"

Obviously you can't inflict status or drop stats on a dead Pokemon, but the self boost wasn't affected by the opponent KOing.
Tested in Gen 2 to confirmed the change took effect, and again in Gen 6 to confirm nothing got changed.