Paul Grundy's, JW facts notes:
In 1971 another significant change came with the introduction of a body of elders. The Watchtower 1971 November 15 p.685 and p.691 said that the Early Christian elder bodies "likely rotated" and so enforced rotation, such that each elder would hold a responsibility such as Presiding Overseer for just one year.
Reference: http://www.jwfacts.com/watchtower/elders.php
Compound Complex comments:
It was a very rough start, what with much fighting and recriminations as to who did and did not qualify, so I heard.
My XJW friend recalls the same thing, in the Sydney congregation where he served (at the time), as MS servant. The Congregation Overseer refused to call the meeting of servants that the society had instructed, apparently, because he feared that the other servants in the congregation would not recommend him as an elder.
I tried to stay out of the bunfight, thinking that if you got involved in all the organisational crap, how could you be a 'shepherd,' caring for the flock.