Nowadays only models of the 925 line are “made” by STAEDTLER.jp, quotation marks because some are actually manufactured in Thailand. It’s unclear why it is like this but this began in the late 70s, since at least 1978, STAEDTLER’s Japanese subsidiary has models that are only sold by them such as the STAEDTLER Chubster 9710, and STAEDTLER lead holder 779 05, pictured below (1978 catalog), later renamed to STAEDTLER 779 15 – 2004/5 Japanese catalog – and also available internationally nowadays as graphite 779 05, appears internationally for the first time in the 1996 catalog.
1978 Japanese catalog and 1996 catalog.
2004/5 Japanese catalog.
Chubster
The OEM is unknown but it could be Kotobuki, STAEDTLER has worked with them in the past.
Yes, the mechanism of 925 25/35 is found in the Platinum Pro Use (MSD-1500B), most parts are actually interchangeable, you can use the grip or body of 925 25/35 in MSD-1500B and vice versa.
EDIT: You can find the rest of the catalogs and download them in PDF format in STAEDTLER catalog scans 1980-2022, you can also find some from the 60s and 70s in the listings I posted in Potential Catalog Leads: Staedtler 1969 and 1978?.