yep that plug is G1, and the blue/white is running to pin 11.
What you describe is really bizare! all the abf looms I've worked on have the speedo sensor on the engine side of the loom to the big round plug on the front of the engine (i.e. the bit with ecu temp, isv, injectors on etc) so deffo part of the engine loom. is this loom definitly a MK3 ABF one, and not some random SEAT model? If it is a MK3, do you happen to know what year it was, maybe there is a difference on the really late ones. Oh, maybe it was it an automatic, if they ever existed?