yeah I noticed that as well, us previous purchasers only seem to have access to the free files now and with no way to pay to upgrade without buying it all over again for $20...
Fairly certain that tier is just dead, I ended up buying it again for the $20 price because the game was good enough in my books to be worth spending 30 in total for the content. I think that *maybe* a slight possibility the $10 tier still gets it earlier than public but still later than $20 as I recall this issue having been brought up a long time ago, but I don't fully recall. I seem to remember there was some weirdness with sale prices not counting towards the required money spent towards the rewards or something (like if it was 50% off of 20 bringing it down to $10 it would only count as $10 rewards) and I don't believe that ever got fixed so I think the tier just got bumped up to 20 a long time ago.
So ye I even asked on the discord, no reply either (and yes the dev did respond to other questions since).
Considering how many people ask about that here more or less regularly and even if I go out of my way to get an answer on this, at that point I just have to assume it's being ignored on purpose.