From the above I could not figure out whether the 8375 / 390544-01 is a 2MB or 1MB chip. Is BBoAH correct with the 2MB spec for this chip?
Most of the times it is referenced as a 2MB chip but in this datasheet (390544-01_8375_Agnus_specification.pdf (amiga.serveftp.net)) (also found on this site) this particular chip is listed as a 1MB chip.
The 390544-01 is definitely a 2MB part. It was used in later production A500+ and A600, both of which can address up to 2MB chip memory (expansion module fitted). The datasheet appears to be preliminary information from Commodore. It also lists various parts that were planned, likely as drop in replacements for earlier 8372 variants, but were never produced. Only the -01 (PAL) and -02 (NTSC) versions of the 390544 were in production.
It's worth noting that the 390544-0x is only pin compatible with the A500+ and A600, and some third party memory expansions. It's not pin compatible with A500, A2000, A3000, which uses the slightly different 8372 pinout. To confuse things further, *some* variants of 8375 (318069-1x) were pin compatible with the 8372 pinout.
For reference, I've found the information on this page to be accurate:
https://bboah.com/index.php?action=artikel&cat=51&id=2174&artlang=enAnd here's a photo of a PAL A500+ using the 390544-01:
https://bboah.com/images/download_photos/a500plus_rev8a1_3.jpg
