I realize what I am about to say could be interpreted as an embittered old veteran, insisting that "These new guys aren't as good as we was". However, when the elder arrangement first came in (c.1972), I can recall ones who did have an extensive ( perhaps even impressive) knowledge of the bible.
Conversely, towards the end of my time with the JWs, the typical elder came over as well versed in WTS procedure - but rather lacking in knowledge about the bible, or even about their very own JW doctrine. There were times when one elder I was familiar with would direct questions about JW doctrine to me, who wasn't even a ministerial servant!
That the earlier breed of elder often had a sound biblical knowledge had little to do with the JWs. Most were converts, rather than "born ins". Also, they grew up during a time when practically everybody was a regular churchgoer, and most people actually took some interest in the Christian teachings, biblical doctrine etc. I would hazard to guess that at least a goodly part of their bible knowledge came from their time before "coming into the Truth." (Of course, how such persons managed to be sucked into the JW cult is quite another story!)
Bill