Do NI test to VOSA standards ? Or different test ?
As Erm said, the manual is vague, it says they must work if fitted i think, not that they must be fitted. As if they are failing it on that criteria, it says the same about self levelling units for them.
It also says you may not be able to test these items or deem if they are working.
An aftermarket kit would usually plug into OEM plug, so id guess they have cut and made whatever connections they needed. Its only 2 wires you need anyway, so easy enough.