Immunologically, I don't think there's any case where delaying a booster has negative effects other than, of course, you spend a longer period without its protective effects of the second dose. Most people have sloppy adherence to vaccination programmes, get jabbed whenever, and yes, batches and types get routinely mixed up with evident ill-effect.
It's a valid point that we don't know, of course, but given the logistical challenge, as pointed out in that article, sometimes we have to take educated guesses. No vaccination means no protection at all.