Someone suggested maybe to have a dedicated thread for this aspect & I thought it might of interest to some - not sure if it's really needed so mods, feel free to delete if not required:
People can post confirmed examples and I can keep this first post updated with the different allocations for each route involved?
Abellio:
8520 & 8567-8568 - Route 481
9410, 9411, 9421, 9424 & 9505 - Route U7
DE20062-20063 & DE20065 - Route 481
Croydon SCH Buses (Arriva and GAL routes) -9401, 9404-9406 & 9408
8121-8124 & 8141 - Routes E5, E10 & E11
8125-8127 - Route 367
8138-8139 - Route H20
8140 - Route H26
8569-8570 - Route 290
8806 - Route R68
8807-8808 - Route H25
8809 - Route P5
8845, 8856-8857 & 8860 - Routes 130 & 201
8847 & 8863 - Route E7
8861 - Route H28
Arriva:
ENL21 - Route 325
T36-37 - Route(s) ?
CT Plus:
DAS1 - Route 309
MX14FUT, SN15LKY, YY15NHX? & YX65RHK - Route 309
Optare Metrodecker demonstrator YJ16DBO? - unidentified route(s)
Go-Ahead London:
E133-134 - Unidentified BX route(s)
EN13 - Unidentified garage & route(s)
EN15 & EN17 - Route 353
SE7-9, SE24 & SE93 - Unidentfied MB route(s)
SE10 & SE16 - Unidentified SW route(s)
SE13-14 - Route 493
SE29 - Routes 300 & 376
SEN38 - Route 434
SEN44-45 - Routes B11 & B16
SEN46-48 - Route 355
SEN49 - Route 225
SEN50 & SEN55 - Unidentified route(s)
SEN51-52 - Routes 153 & 232
SEN53-54 & SEN56-57 - Routes 300 & 376
970 (Ensignbus) - Route 679
972 (Ensignbus) - Route 656
973 (Ensignbus) - Route 687
975 (Ensignbus) - Route 667
Metroline:
DE1585 & DE1603 - Route 242 (Herts)
TE880 - Route 84
VWH2703 & VWH2705 - Route U4
RATP:
DE20030-20031 - Route 413
VN36130 & VN36138 - Route 642
VN36135 & VN37961 - Route 698
Stagecoach:
36012, 36041-36042, 36044 & 36060-36064 - Unidentified route(s)
36043 - Unidentified RM route(s)
36065 - Route 638
5 363* series Enviro 200's ex Route 323 - Unidentified route(s)
36376 - Unidentified route(s)
36378-36379 - Route B14
37502 - Unidentified TB route(s)
47632 - Route R7
47638, 47641-47642 - Unidentified route(s)
47847-47848 - Unidentified route(s)
47974 - Unidentified route(s)
48024-48025 & 48031-48036 - Unidentified route(s)
Tower Transit:
Sullivan Buses:
One from AE11-16 - Route W9
E54-62 - Route 617, 629, 626, 692, 699, 640, 628. And two each on routes 683 & 688
ELV7-9 - Route 617, 629, 626, 692, 699, 640, 628. And two each on routes 683 & 688
TPL926-927 - Route 617*, 629, 626, 692, 699, 640, 628. And two each on routes 683 & 688
UNO:
606 - Route 395