No 'double standard' 'emerging'.
Nice and simple: Of course you can paint your aircraft anyway you want. If you choose to paint it in a tribute scheme, or in a historical scheme, then it makes sense to bother enough to try and get it right.
If you are an organisation claiming to be undertaking a tribute, or honouring veterans or teaching history, then yes, you should be held to a reasonable standard of historical accuracy, including painting the scheme as accurately as possible.
To expand a little: Deliberate variations, where undertaken for good reasons ('Ol 927', the names on the Collings bombers, the CAF's tribute C model Mustang) obviously make sense I'd suggest - nothing 'wrong' and a lot 'right' with them. Adding D day stripes 'because they look cool' over an authentic scheme's a little odd, but hardly a big deal. At least you are looking for cool. Making a scheme up, as OP's saying; nothing wrong with that. As a big Sea Fury fan, I think the 'Spirit of Texas' on Stu Dawson's is very neat.
Making a poor effort through not even taking five minutes to research the scheme on the Internet, such as the CAF's Martlet, shows a level of lack of respect, shows ignorance of the supposed subject of the 'tribute' and is an insult to the service. Making up stories to cover that lack of a decent job's even worse.
It's not hard.
Regards,