There have been no updates to the NAC 202, 282, 252 and 552 since they were first introduced to the market 18 or 19 years ago and people are still buying them. A testament to the appeal of these gear which have stood the test of time. The NAP power amps are also very good although they were revised with the DR update not too long ago.
You could well argue that the pre-amps were also revised and upgraded by virtue of the DR upgrades to the pre-amps (remember that the 552PS DR is part and parcel of the NAC552).
Whilst that is my view unless you have analogue sources, much of what I’ve read on the forum seems to indicate that NAC is key to getting the “Naim Sound”?