Smudge,
as I recall the externals were in constant use from the very first.
The fuel gauges were very unreliable and the capacitance test equipment non existent at that time. So we had three fuel states. Full mains, full mains and auxs and everything plus externals. All wing tanks had to be overwing checked as full. As I have mentioned before the visiting USAF Herc chaps gave us priceless info at the beer calls they attended at Fairford.
Yes we had tech hiccups mainly due to the RAF tradition of only type training a very few of the 'techies'. The rest had to use their basic trade skills and get the not very good manuals out for fault finding. Naturally this took time so even a minor snag could take ages to fix.
As Dean says most of us were under the impression that MOD were warned about non use of FSII and for the usual reasons chose not to add it to RAF fuel. Again in a previous thread I have mentioned our pre FSII water in the fuel freezing over northern Canada.