This fixes an accounting issue where expenses or revenue deferred to the same month one year later were not spread as expected. Businesses can now rely on annual deferrals being created correctly instead of amounts remaining entirely in the original month.

Before this change if you wanted to defer something to exactly the same month in one year, it just deleted the deferral entries and left the expense/revenue in the month of the move.
Same issue for Odoo 17 and so on