I think a more relevant issue, is that the longer the time between sheltered water lessons, and open water lessons, the more the students skills deteriorate. This is no reflection on the student, or the instructor. It is a fact.
Experienced divers skills deteriorate after a prolonged period out of the water, they have the advantage that they have embed skills learnt and practiced over a prolonged period of time.
We have a similar issue in our club, we have a group of students, who learnt over the winter, and where supposed to progress to open water in April. We had the lock down, and even thought this has been lifted, currently, no teaching is allowed. We are discussing how we support them and encourage them to continue once 'things return to normal'. Additional tuition to bring their skills back up to scratch, is not an issue, we have the instructors, and facilities. The bigger issue is maintaining interest and enthusiasm over another winter.
Gareth