Lots of militaries do that. Look at US; B-17, B-52 before the B-1, B-2. M-60 before M-1. etc, etc. As long as the designation is unique, it really doesn't matter.
Before 1948, the US had separate and independent departments for each branch of service, and with the vast proliferation of different designs during and immediately after WWII, the numerical designations climbed to inconveniently large figures, while the same equipment become designated by different nomenclature when used by different service branchs.
This is why after the major branches of services were unified under a single department of defense, the DOD undertook to scrap all existing nomenclature schemes for the different branch’s in 1960, adopted a single unified designation scheme for all branches and start all sequences from 1, and included all equipment them still in service.
Hence B-1 came after B-52, while F-4 came after F-111.