Hi Michael,
The top 3 are correct.
Neither Gatwick Express nor Heathrow Express charge an off-peak fare at any time. They are railcard discountable, and you are correct that Gatwick does seem to allow the discount in the evening peak. That may be a mistake. HS1 is technically outside the zones which is why they don’t allow off-peak in the evening.
I don’t know what the arrangements will be for the new extensions of PAYG.
