The bass does not have mellow filters.  What you are looking at are volume trim pots.  Those are screwdriver set trim pots that are usually found on the rear of Series 1 basses with PF6 electronics.  This bass has PF5 electronics which has those controls mounted on the front.  
 
From what I understand the last bass with PF5 electronics is bass 73-47.

I've wondered a loong time what is actually the difference between the PF5 and PF6?
 
And btw; mellow filters..?

Fantastic.  Play it well!

Eiji, thanks so much for sharing your knowledge on the Logos and Alembics. Just purchased a floating A Logo small bodied bass and I am so glad to know where they fall.  You're the best!   Todd