@Lute
Also when your doing your sluething ....here are some known Japanese quad matrix labels to watch out for ;
KING , MINORUPHONE , NIPPON COLUMBIA , POLYDOR KK. ,TEICHIKU , TOHO , TRIO , PIONEER , WARNER/PIONEER ,
AUDIOLAB , SONY , SANYO , TOSHIBA , TOSHIBA/EMI , TOSHIBA/PROBE , CROWN , YAMAHA , SANSUI , ERATO , JVC
VICTOR , RCA , MOTOWN , AVCO , GLOBE , RANWOOD , MUSICOR , MILESTONE , PHILLIPS , A&M , LONDON ,
RARE EARTH , VANGUARD , and CTI .
Whoops forgot : PHONOGRAM , PHONOGRAM/MERCURY .
In addition there may be a few obscure labels . I'd definitely check out the Samplers.
As to matrix formats , both SQ and CD-4 should be easy to spot , as would QS and UD-4 .
Some others may be QM , QX , RM , 4D , 4M , QUADRA , 4X , MS , M4 , S4 , and probably a few others , I can't remember. There could even be some that simply say compatible with Sansui , or Sony quad , or Stereo Compatible Surround .
Happy sleuthing ,
Fizzem