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The best I can come up with is that they are pre-1960 CCa:
For the old "Gray-Plate" early 1960's SIEMENS HALSKE E88CC and CCa:Make sure you are buying Real Siemens Halske CCa = E88CC / 6922 tubes - They have the double-stage getter frame-grid construction, Gray separator or Gray Electro-static shield, 4 seams on top and numbers in the glass between the pins and the Siemens & Halske S+H logo on the front of the tube
with "painted serial numbers" for the pre-1960 versions
and ACID-CODES for the 1960 - 1965 versions. After 1966 the acid-codes may change to codes stamped on tiny metal rectangles soldered onto the sides.
They are tube production designation codes. LOL, for you newbies... and almost all of you are. The venerable 6DJ8 tube had many replacements, If you don’t know what type of equipment it was used in you can stop reading here. It was a superior voltage amplification tube to coupe with a amperage amplification amplifier. Actually, the year and vintage I cited was the best ever mad according to all reliable sources.
op asking for help yet being condescending... nice...
having said that -- this is a case where being able to post a pic would be so helpful