In the UK, if you buy a blu-ray only disc, you get the new masters on that blu-ray.
in the US, if you buy a blu-ray only disc, you get the 2011 discs repackaged. The only way to get new masters on blu-ray in the US is to buy a 4K disc that comes with the new masters on the pack-in blu-ray.
It’s pretty much pot luck if you buy the single blu-rays in the UK. Amazon, you’re not guaranteed to get the 2020 version. At HMV, someone i know purchased the OT as separates. ANH was 2011, ESB was 2020, ROTJ was 2011. HMV refused to take the 2011 discs back as the package was opened. So he ordered ANH & ROTJ from Zavvi. Got ANH 2020 & ROTJ 2011. The packaging is identical too so there’s no way of knowing which version you will get even if you go into a shop and check the covers. So now he is stuck with 2 versions of ROTJ and no way of knowing if he buys another copy if it will be the new version or not. Until all the old stock of the September 2019 releases are sold, its a risk buying them as separates.