I believe I was using Google to log in (I did recently lose a heap of passwords) and I do have another Google account attached to firstname.lastname@example.org
The only other email an account might be linked to is email@example.com which is the old work email. When I login in to Google using firstname.lastname@example.org and then go to Feed Burner it welcomes me as s.<email@example.com.> Incidentally all of my Feedburner feeds are missing too - though I can see they are still working and active for subscribers. Panic.
I used to have another Google account attached to firstname.lastname@example.org but I deleted that one months ago.
Does this help? I don't have any usernames except for creativelearningscot but that seems to have wandered off (I think it still exists in YouTube world).
If your question was asking specifically about the Pipes IDs, I had 14 pipes I think