I started reading the Marvel G.I.Joe comics around issue #36, but through back issues and reprints, managed to read many of the earlier stories, including the original first issue. And I was very aware of the mysterious 14th Joe shown on computer in that issue:
But leave it to comics fans to give that in-joke a backstory.
It's a interesting twist on the story and I like the idea that there was a secret member than no one else knew about. Although, since that was in the Devil's Due line, that's probably alternate continuity now...
For Shooter, I used the SHIELD Agent Heroclix.