Animation Source Forums

I wonder if it was possible that Baloo had met Don Karnage before Plunder & Lightning?

It's not very clear when you watch the episode; but the answer seems to be "no". When the air pirates are chasing Baloo the first time Kit gets onboard, DK refers about Kit but never says Baloo's name. ("They make me so angry!")

Although it's pretty clear that Baloo did encounter the air pirates before, because he knows very well how to counter them and he's not very surprised to be attacked.
When Kit is tied down, Karnage says "you're protecting your friend, we will find him" again not saying Baloo's name.

Finally, he says "the round furry pilot and the annoying business lady" when he kidnaps them in part 3, which implies he doesn't really know Rebecca either.

I'll have to watch Plunder & Lightning again, but that seems about right.
In any case, he learned about them quite enough in the following episodes

I think it's safe to say Baloo encountered Karnage several times while he flew his own cargo.

Before Karnage knew Baloo's name he just referred to him as the "Round furry pilot" or "Fat" pilot.

I'll have to run P&L again.

Yeah, I think he already encountered the air pirates; he just didn't encounter Karnage "personally".

You all make sense, they wern't on a first name basis but have had a few close calls and encounters.

Cargo pilots and pirates would have some contract since it is a job.