First, you simply do not know that your nails have properly cured. You know that they are hard, and that's all you know.
You know, I am as critical of CND as anyone could be, but it's just insane to ascribe the requirement to use a CND lamp to a "conspiracy," "brainwashing," or "a trap." Anyone who knows the science of how gel polish works knows that Shellac has some unique qualities that impact curing. CND designed the lamp to compensate for those and require you to use it. That's not a conspiracy; that's the act of a responsible manufacturer.Not doing that is the act of an irresponsible service provider. And you certainly cannot be a CND Shellac certified professional if you are not using the CND lamp.
BTW, there is a difference between having insurance and being insured. I don't know how the system works in the UK, but here, if you have a claim and your insurer "discovers" that you knowingly deviated from the manufacturer's instructions, you may be surprised after years of payments, to find your actions defined as "negligence" and your insurance invalidated.