(04 Jul 2022, 7:52 pm)Storx wrote Aye believe there's patterns down in Stockton aswell if I'm right between both Arriva and Stagecoach

3 - 5 - East Cleveland Services
8 - 20 - Middlesbrough / Thornaby Local Services
20's - Nunthorpe Services
30's - Billingham Services
40's - Unused
50's - Stockton Local Services
60's - Redcar Services
70's - Unused
80's - Guisborough Local Services
90's - Whitby Services

The 7, 39 and 61 are a bit of an outlier and the X66/X67 again but suppose they follow the road so makes sense. X12 is arguably a Middlesbrough service so kind of fits there.

X12 is just the result of combining the X1 and X2 together. Probably fits within the X10 series of numbering for Newcastle-Teesside services.