I've manually checked all the SERengine ones, but there might be more:
At least Bravenet and Slashdot accounts are not being exported.
I select all of my projects, do a Modify Project > Export > Account Data and take care not to check "just verified" or only certain engines", and search the result: no Bravenet or Slashdot accounts at all.
But when I go through all the verified URLs (thank God there is a sorting by engine), I find quite a lot of them. And when I manually check the project.static files, I also find the account data there.