My understanding is the Annual Parish Meeting / Assembly should take place between the inclusive dates of 1st March and 1st June. See:
https://towncouncillor.com/14848/months-parish-council-suffolk-their-annual-village-meeting
What we do, in an election year, is simply set the date (for May) and ensure that the date is publicised and invitations go out, but nothing else, As an assembly, and not a council meeting, it seems obvious that it should be forward-looking.
The other problem with setting it in April is that you are then in a 'purdah' period when I'd have thought it's best for the council (which has to arrange the meeting) to avoid providing a formal opportunity for candidates to big themselves up.
However, yes, you do make the point that there is often a formal report in the meeting on the council's achievements in the previous twelve months. But there is no reason that that should not still be delivered, even by an outgoing councillor. The new councillors may be very interested to question it!