Hi, been through a lot of tube identifying pages and info, so i'll try to read out the code.
But deeper one gets in to this stuff more concerned one should be about few things. First lot of manufacturers relabeled stuff back in the day so your tubes could be "real deal". But there are lot of fakes out there, they faked them already back in the day and there is a good writing in net about it by re-seller of nos tubes. Apparently all the old factories printing machines for markings are used by fakers today to re-label tubes, and someone is even laser carving those telefunken diamonds to tubes.
All this has made me very careful when looking for tubes.
But back to that code, PA1 L6K, viser correct me if i get it wrong. PA means tube type DL-92, 1 is probably factory code for variation of this type of tube, L is factory code it's Mazda factory in Bruxelles, France, 6 is year code and K month code.
-Tatu-