[UPDATED] 07/09/2022
Taking the discussion on the matter into consideration, we’ve decided NOT to make Personal Reserves from Season IX Base rewards time-limited after Update 1.18.1. Therefore, ALL Personal Reserves you obtain as Battle Pass Season IX rewards will have no expiration date, whether you collect them before or after 1.18.1 hits.
Regarding time-limited Personal Reserves in general, we will introduce them as an in-game entity with Update 1.18.1. Yet we have no plans to use them in in-game activities in foreseeable future.
Once the new mechanics are introduced, all Personal Reserves on your account will be converted into the new reserves at no loss of value. Expect a dedicated article on the new Personal Reserves in the coming days.