I think the very first people vaccinated got (close to) the initial time-frame to the second dose. But, yes, it fairly soon switched to "We'll see you in 12 weeks", because of a preference (that I'm still not sure added up) to spread the half-vaccinated status to more people further down ths list, quicker, at the expense of no longer treating the prioritised as a priority to complete the course. Not currently sure if that was Pfizer/BioNTech as well as AstraZeneca/Oxford (which is definitely elongated) and what the plan is for the only just started Moderna doses that haven't even reached its recommended 4-week 'in vivo' in anyone given it under that standard authorisation.
I know someone who has just had their second AZ jab at about 10 weeks, though. Expected it in a fortnight. That might mean we're actually slightly above the number of doses realistically expected to sustain 12-weeks. Or vaccine refusal/un-soughtedness is higher than expected due to the bad press, boostering the shot-slots available for returnees. Or both.
(My own expectations have been bouncing around between as late as August, at some points, down to date we've now passed, at others, as to when I'd be asked to book. I'm at the younger edge of the pure age-priority ranking but also no (known) health/support issues, so I'd be very happy to get the nod but know there's others who are probably net better off getting my theoretical earliest slot, instead of me. I think if I were chasing it with enough force of argument, I could have wangled a date by now, if not have had the primer already. I still think it was a bad decision to not do any non-medical keyworkers (police, teachers, bus-drivers...) in advance of their personal age/health positions, as well.)
I can't tell you right now what the statistical result of all this messing about (or lack of it) with the authorised schedule actually is. We seem to be firmly out of the latest wave (and that even with incidence of the UK-variant, pretty much by definition), but disentangling treatment and lockdown (it's hardly been two weeks since the first stage of relaxation) is way beyond my paygrade, as a calculation.