Interesting question:-
I can find no mention in 60601-1-2 to 'sample size'.
But it does use CISPR 11 as a 'basic standard' for methods, and that standard does use a sample (of between 5 and 12) for serial produced products.
I have never done testing on anything other than a single device, and this has never been an issue, either with our (very experienced) test house or our Notified Body. So, it is tested as if it were "Equipment produced on an individual basis".
Just remembered -
60601-1-2 is a collateral standard to 60601-1. Clause 5.2 of that (Ed 3.0) standard states:
Type Tests are performed on a representative sample of the item being tested.
So, as -1-2 does not modify this clause, it remains valid.