Any profit you make will count on the books for that season but that season will remain part of the calculation for the next two years too but yes you are correct that if you sell big in Y1 and then spend big in Y2 then even though the numbers balance that could become problematic when Y1 falls off the calculation. However, remember that spending is amortised over several years anyway, whereas sales go on the books only once, so timing your sales is more important than timing your spend.
So it makes sense to sensibly balance the timing of your sales in particular. In our position, we may have to sell a player before the end of the year to balance the year. But what you don't want is overkill - if one player (say Onana) can balance this year's PSR then don't also sell Branthwaite until the next financial year, as essentially, you get one more year out of that profit that way.
