It is an abbreviation for special. Turns up from time to time in the book. What makes the camera(s) special isn't spelled out. The book is very terse.
Thanks Dan, I assumed that was probably the case but wanted it clarified.
So we a have a camera here that's non standard and an entry for the same serial number that's one of six "special" as in non Standard Speed Graphics. Maybe more than a co-incidence
Then a non standard camera from Speed Graphic parts *except for the shutter) which isn't in any of the Graflex catalogues so has no model name could well be a Spec. Speed graphic.
Ian