Logic Pro X apple loops and midi files


Hi. A few years ago I took a large collection of GM drum midi files. I loaded them one-at-a-time onto a software instrument track, picked the Socal kit to play them back and saved them as green apple loops. Recently I decided to try one of those loops with a different kit. I dragged the loop onto an instrument track, then deleted the Socal kit and loaded a kit from SampleTank 4. When I did, it wouldn't play back. I checked to see if they were on the same midi channel and they were. Still the midi would not play back. Then I found the original midi file, opened that in Logic, and re-loaded that same kit from SampleTank. Worked perfectly. So my question is what is the process of saving a green apple loop doing to the original midi file so it will only play back on the original instrument it was saved with?