Hello Johannes Pieper, I just started in Land Biz but there was a similar conversation in the Masterclass private Forum, started by Justin Hunter.
The main outcome from that conversation was that, if you decide to operate in a non-disclosure State, all you can do is to "shape" your offer according to all the sources that you can find available and that may not include the SOLD comps. This essentially means, for example, to refer to a reliable local realtor and/or use active listing pricings from zillow, realtor and similar having care to discount them appropriately (and probably a book could be written on what "appropriately" means....). There are also software tools that can facilitate a lot the pricing part: priceboss and prycd are the two I know but a subscription is required.
I'm aware this might be not the answer that you were hoping for but I thought it could have been someway useful for you to know.
Have a great weekend and good luck!