It doesn't say it's only for the new models though.
I see a 2 year service interval in the manuals for the Perdix 2 and Petrel 3.
I see a 5 year service interval in the manual for the NERD2.
There is no service interval specified in the manuals for the Predator or Petrel or Perdix, but I recall, when they were current, reading elsewhere and being told by Dive-tronix that they were supposed to be serviced every 5 years.
Where do you see a service interval specified that gives an indication that it applies to older models?