The accepted standard for MIDIS is melody on track/ch 4, and bass on track/ch 2 with piano on track/ch 1.

Usually any harmony note tracks (those that will drive harmonisers) can be found on track/ch 5.

ANY commercial file will be set up this way.

Anything else different is an edited file. People who post MIDIS should stick to the standard. But sadly they don't as so you get this confusion with the files downloaded from "non-commercial" sites

Dennis