Look at the link to the Vintage Knob. It has a very comprehensive list of contractors and their Identification code. It's likely just a partial list. To know how complete it is, we need to start tracking serial numbers of models that have the T-Tag on the ID plate.
This is lifted from Axle's thread:
SOC (Sansui amps like AU-888, BA-60, BA-100, TAC-505, SAX-350D, QR-1500)
NDS (Sansui amps like AU-777D, BA-60 and BA-90)
AZUMI (Sansui amps like AU-D907X Decade /707XCD /607X /A607i /A707i /A507i /A707Extra /D507X /A707L /A777DG /A909 /E710 but also k7 decks like SC-A33 ; Aiwa CDS-505). Murata has a subsidiary specialized in EMI suppression filters named "Azumi Murata" in Nagano but I doubt they are or were the same.)
ARS DK (Sansui amps like A-515, the latter also seeing a run at regular "Sansui")
Nagano D (Sansui dual-k7 and amp like A-M7 or AU-D55F, timers like AT-212)
Miharu DK (Sansui A-M90 and A-900XV ; also active with Onkyo)
S.Kokusai (Sansui TTs like P-D31)
Kokusai Denshi (Denon DR-F6)
Shinetsu (Sansui TTs like P-E300 /E302 /E710 /M70 /L75)
ORION (Sansui SE-9, A-5001 /3001)
MSC (Sansui TTs like SR-3030)
To be clear Sansui manufactured most of their own equipment. It's likely they just used contractors for overflow, low production or specialized equipment they didn't want to spend the development money to set up in-house production lines.
We have serial numbers recorded in the Serial Number Database that don't follow the standard Sansui format. It's likely these models were produced by contractors.
- Pete