GWR Peak Time Advance Quotas from Stroud line

[Nunners]

I've been looking at flying out from a London airport (any of them) on the 4th and 14th of July, arriving at the airport late morning. A week ago when I first looked there were decently priced advances from Stroud / Gloucester / Cheltenham to Stansted, Gatwick and Luton. When I look now, these advances are no longer offered. However, the identical advances are offered (on the same trains!) from Swindon. Surely there has to be a mistake made somewhere here? Bristol Parkway offers decently priced advances as well.

Any help would be appreciated.

 

[Hadders]

Advance tickets are quota controlled, it's probably the case that there are only a handful of cheap Advance tickets from Stroud and once these have gone they're gone.