"The WE-8000 is the only SAEC tonearm where the offset of the headshell is correct.The SAEC 506/30 was designed to be used with 10" and singles only. It’s geometry does reflect it. Out of curiosity I have calculated a different alignment for the 506/30 which does suit 12" records MUCH better" - @dertonarm
I’ve been thingling about that statement made by Dertonarm. Looking at my SAEC SS-300 mat i can say that even this mat was designed for singles (7’ inch records) and LPs.
http://img.ukaudiomart.com/uploads/large/1850936-rare-saec-ss300-special-alloy-mat-870g-made-in-japa...
This is the ONLY mat that i know with special concave for 7’ inch records while the other mats are totally flat. I believe SAEC did a great job for professional market back then.
As i said earlier if it was made for radio stations then the main format for new material on vinyl is SINGLES (7’ inch records), all promo material for the radiostation released by the labels on singles to promote the best tracks from the LP long time before the LP will be even pressed or available for sale. This is how the industry used to work back in the days. Singles with signs like "promo use only or D.J. copy" is typical for any radio archives. One song per side, about 3:50 min only, 45rpm. I believe @dertonarm is right at some point with his statement about SAEC tonearms, but i can just add that SAEC mat is also designed for singles! Think about it.