I did not read your blog, but based on your thread title.......
The worst thing you can do is use an mp3 for collaboration.
I hope this is the last time I need to point this out (probably not) as I've done numerous times.
An mp3 has about 72 samples at the beginning of file that is not present in a wav file.
So you collaborator is immediately out of sync no matter what (s)he sends back to you. Compound that with your collaborator send her/his mix in an mp3 to the next collaborator and that collaborator is now out of sync and sends you a wav for the final. That wav is now (at minimum) 144 samples out of sync with you.
One caveat, atmospheric or free form Jazz may not experience the out-of-sync as much as tight EDM or Rock or Prog or Metal.