AP, true.
The Nimrod 1 had a series of software updates.
Off the top of my head, when we started the OCU we were on version 1.3. 1.4 came out during our time on the OCU but the staff ensured we remained on the earlier version to avoid confusion. On the sqn we learnt 1.4. A few months later 1.5. In half the time after that, 1.6. Then we got a new airborne programming system and got updates at 6 week intervals or less.
Then came the Mk 2. Naturally the Mk 2 software standard was frozen at a point during production and delivery. It was less capable than the Mk 1.
After crew conversion and new updates the Mk 2 soon proved superior.
It is the same with any new kit.