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What you linked can neither confirm nor deny it. Nothing about price parity.
But there is ongoing lawsuit about Valve allegedly forcing devs to set same price:
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And there some rules about keys:
So yeah Valve is a good guy, but you don't want to mess with them and trying to scam them or Steam users, that one they state clearly. Even big publishers like EA or Ubisoft offer similar prices and deals for their games on Steam, because they know they will be kicked out for not playing nicely.
So yeah if you offer your game "for free" to 5$ Patrons, but it's sold for like 10$ on Steam you are in a trouble. And I doubt it matters how long people paid said price and how much they was milked before
