X10 allocations from when GNE took full responibility of the route....
Leyland National Mk2, MCW Metrobus Mk2 or Leyland Olympian / ECW - usually vehicles that were DP seated, though bus seated Cummins L10 engined Leyland Olympians did appear.
DAF DB250 - Optare Spectra - spare vehicles were normally DP ECW bodied Leyland Olympians.
Volvo Olympian - N-C Palatine 2 (3828-3831) - spare vehicles were normally the N-C Palatine 1 bodied Volvo Olympians (3940 being one), though MCW Metrobus Mk2 (bus seated versions, much speed down the A19.... not) and Scania L94UB - Wright Solars or Volvo B10BLE - Wright Renowns appeared.
Volvo B7TL - Wright Eclipse Gemini 1 (3941-3943) - with Volvo Olympian - N-C Palatine 2 spare. Single deck subs were Renowns or Solars.

X9 was introduced adding Volvo B10M - Plaxton coaches (1x Expressliner and 2x Paragons), spare vehicles were often Volvo Olympian / N-C Palatine 2

Coaches were found unsuitable due to extended loading times and accessibility so the allocation for X9 / X10 was streamlined into one vehicle type starting with....
Volvo B7TL - Wright Eclipse Gemini 1 (3941-3943 / 3962 - 3965) with Volvo Olympian - N-C Palatine 2s being the ever reliable spares.
Volvo B9TL - Wright Eclipse Gemini 2 (6043 - 6048) spare was B7TL 3963 in Tyne Tees Express livery and 3964 in a variety of liveries. Volvo Olympians still appeared.
Volvo B5TL - Wright Gemini 3 (6308 - 6314) with fleet livered Volvo B9TLs as spares, though anything could appear like Solars and Citaros.
Volvo B11RT - Caetano Levante - Intrim vehicles until the Elite-i were ready for service.
Volvo B11RT - Plaxton Elite-i (7150 - 7156) with various Volvo / Caetano Levante Coaches acting as spares, along with Wright Streetdeck.
ADL Enviro 400MMC - The next residents of the A19 Express?