I like the approach of the suite of plaques, but I think it begs the question of whether there should be an overall citation for Bell Labs that explains the research environment for contributing to so many IEEE fields. (I'm in favor of one.)
I suggest eliminating the first 11 repetive words from each of the plaques. This frees up 11 words that can be used to explain the impact these discoveries had on the field -- moving the citation from simply a list of achievements to explaining the effect of those achievements.
In addition to eliminating the repetition, I suggest varying the introductory wording "Discoveries in, Contributions to, Advances in, etc."
Why is the proposal for the first 60 years? Is that simply to adhere to the question of whether the achievement is more than 25 years old, implying that 25 years is a marker of being historical? The general public will probably find this dating to be arbitrary, more accustomed to seeing first 50 or 75 years. I would suggest going with the first 50 years and lopping off achievements that fall after this date (giving more room to explain impact of earlier discoveries). If the date range is kept as is, I suggest making it 1925-1985; regarless of how you may count inclusivity, generally people will think 1925 + 60 = 1985.
In response to Ggcooke, the 1st transistor already has its own milestone, so I would remove that from the Solid State list. If other of the discoveries are worthy of individual milestones, I would support a system that would mark those milestones at different locations, such as place of implementation & linking it to a specific impact.