I was really into trade-skills in the Velious era on live, and back then it was established "fact" that when you did a combine success or failure had no bearing on your chance of skilling-up. However, this is not true on P99 or on live, where successes have a higher chance of giving a skill-up.
It's possible that people in classic got it wrong, but they tended to research stuff like this, so I think there's also a chance that the game mechanics changed at some point. Unfortunately, because the Wayback machine doesn't archive the tradeskiller's forum posts, I haven't been able to find proof one way or the other.
What does this have to do with you? Well, if you want to spend some time on Google, the Wayback Machine, and similar sites (see
Nilbog's guide) all you need to do is find evidence (the kind Nilbog would accept) that explains the contradiction. Post it here and you'll help make the server more classic, or at least dispel an old myth ... and be 5k plat richer in the process.
Just to be clear, you get the 5k whether you find proof that the idea is a myth or that mechanics changed: I just want a conclusive answer.