There are now wide timeframes emerging from 3 / 4 weeks in the USA and most parts of the EU, through to 12 weeks in the UK and 16 weeks in Canada and Spain. But there are two aspects in common here: though the 3 / 4 weeks is a minima, in no places is it the maxima. So even in Germany the second dose can drift out a week or two. Secondly, if you are late for the second dose in all of these countries, then you simply get the second dose at the time you present yourself, and the course of treatment is considered complete. The only circumstance you would end up with 3 doses outside a medical trial, and leaving BoosterVax out of this for the moment, is if you had the second dose early, so before 3 weeks in the case of Pfizer. That second dose would be considered invalid and the third dose administered after 3 weeks. You wouldn't have to start all over again if you were late with dose2.

From an immunological point of view there are some benefits from delaying the second dose, but that's a broader public health discussion. But you should have confidence in your second dose even if it is a few weeks adrift from the local timetable.