Has the 767 existed before ? Might be getting confused with a 707 that goes that way to Stansted.
Stratford upon Avon was one of them tags like Salisbury on the 032.
I think it did exist a while ago, and it went from Nottingham/Leicester to Stansted like the new 767 will. I don't think it went via Peterborough/Cambridge though, and was probably more than 2 services per day. Back then the 777 went via Milton Keynes / Luton and not Leicester like it does now, and the 707 started from Northampton not Birmingham. I think the 707 and 777 changed to their current routes after the 767 was withdrawn.
Having had a look on the journey planner there appears to be quite a lot of changes taking effect around May, this is what I can see so far (bit difficult because the timetables aren't uploaded yet):
025 - Increased to every 30 mins between London and Gatwick for most of the day (route unchanged - via Heathrow). Service to Brighton remains hourly.
135 - Renumbered to 195 and timings changed (route unchanged).
150 - Increased from 3 to 5 services per day (route unchanged).
170 - Increased from 5 to 6 services per day (route mostly unchanged).
171 - Increased from 4 to 6 services per day with all journeys extended to Manchester Airport and Liverpool.
172 - Increased from 2 to 4 services per day with all journeys extended to Manchester Airport.
196 - New service. Leicester - Nottingham - Derby (2 services per day).
210 - Coventry and Warwick Parkway stops removed, some timings changed (number of services unchanged).
230 - Increased from 6 to 9 services per day. Route extended at both ends to run from Gatwick Airport to Derby.
401 - Daily extension to Frome now diverted to Stroud/Gloucester instead.
451 - Route changed to serve Scunthorpe instead of Lincoln.
452 - New service. Grimsby - Cleethorpes - Louth - Wragby - Lincoln - Nottingham - Marble Arch - London Victoria (1 service per day).
460 - Increased from 6 to 8 services per day. All services re-routed via Heathrow with some also stopping at Warwick Parkway and Earls Court (Milton Keynes, Golders Green and Marble Arch no longer served). Extension to Stratford Upon Avon appears to be removed.
503 - New service. London -Heathrow Airport - Exeter - Newquay - Penzance, not 100% sure if there may be other stops between Exeter and Penzance (1 service per day).
707 - Increased from 8 to 9 services per day. (route unchanged).
767 - New service as mentioned above. Nottingham - Leicester - Peterborough - Cambridge - Stansted Airport (2 services per day).