It's safe to say that the original CK12s in the 414EB were there when the mic was introduced (ca. 1976) and disappeared in the early 1980s.
As I said, many people would like to know more about the birth of their favorite (now called 'vintage', if you can believe it) transistor mics, but I have not found a person or department inside the company who has kept a log. Austrians are different from Germans in that way, I believe. (That's not necessarily a criticism.)
You could do a component search inside the mic's amp and look for that rare component that may have a date code, but AKG used mostly undated larger components and Tantalums as polarized capacitors, rather than elcos with dates, as found in Neumann mics.
The other thing that is unique about the 414EB is that there was never an update (which could thus be part of a database) of the model: the last one looked exactly like the first one, except that it had a higher serial number...