This answer might or might not help. Unfortunately I will refer to a document I read online recently but failed to bookmark, so consider this is more of an introduction to a unicorn than an answer.
Facing a similar problem with forgotten pattern and no clue which of many gmail accounts the phone was associated with, I tried every gmail account I could think of and admitted defeat. I halfway think there was a bug in my old Motorola's software that meant I couldn't have recovered access even if I did know the gmail address, but that's neither here nor there.
Defeated, yes, but still breathing. I hate nothing quite as much as destroying data, so I did not want to do a hard reset. I decided to find out if smudges or fingerprints on the phone's screen might somehow carry a memory of the pattern I routinely used to log in to the phone in the past. I entered various search terms into Google and eventually found that some security researchers, possibly in Israel, had published a white paper on the topic. I was overjoyed, but didn't have time to read the whole thing. I didn't try it and still don't know if it will work for me. (In my case the phone has been handled so much since the last time I logged in that it's unlikely.) I remember that they figured out how to shine light on the phone from a particular angle, but not the angle or anything about the light itself.
So, a lame "hope that helps" to close with, and a promise to look for the paper again if I have some time later on this afternoon. Maybe you can find it using Google.