I found out what was happening with my 0-1023 ProRes:
If you encode a file with video levels as ProRes444/ProRes422, most pieces of software will interpret the file correctly. However, if you encode the file as ProRes444 with full levels or RGB values, most post production software will incorrectly assume your file is video levels and clip values.
So DaVinci Resolve assumes that ProRes444 is video levels and so does Premiere when you import it. Even though, according to the ProRes whitepaper, ProRes444 can encode RGB 4:4:4 data or YCbCr 4:2:2 data.
Even if you did encode RGB 4:4:4 data to a ProRes444 file, your software would still need to correctly interpret that data and not clamp values. This is why these 4:4:4 codecs are so confusing. Premiere in that case would clamp those full range values or assume the file was video range. You still might be able to access those values (by pulling levels down in Max Bit Depth mode for the Sequence), but Premiere isn’t seeing them as intended. As well as "common" media players.
In practice, it makes sense that Premiere would assume that a 444 file would be full range. Full range files are 4:4:4. But that only happens for me with my NeoScene Cineform importer plug-in which is, of course, not out of-the-box and hence always interprets footage as intended based on it's type and meta (if present).