During my dubbie days, 1958 - 1972, there were no such things as official "elders".
We had "servants". These were:
Asst Congregation servant.
Bible Study servant.
(The above 3 were "the committee" and were in charge of DF-ing and probation, etc)
Magazine / territory servant.
However, when the book JW's In The Divine Purpose was released, I seem to recall that mention was made several times about the old days when there were "Elders" appointed in the 30's and 40's. Also, for some of these years, elders were actually voted into office by the congregation!
The new servant arrangement was hailed as being an advancement on the old elder system. So, it was with considerable surprise to many when the Society reverted back to it. I also recall the lead up to the second elder period when the term wasn't used much, it being commonly referred to as "Older men" of the congregation.
I'm hazy on all this change that took place around the mid 70's and would appreciate any info you might have.