I expect the need for consultation with retired engineers relates to understanding of how the manufacturing challenges were solved in the past.
If plans were initially designed with those legacy manufacturing techniques and tools and equipment and skilled technicians in mind, then there may very well be a need to have the retired engineers explain those contextual assumptions to the newer engineers.
I expect that there may have been a lot of "why did they do this this way?" conversations.
The older plans may also have referenced sub-assemblies that were then available from third parties, but are no longer made.
Sort of like modern automotive engineers having to have carburetors and manual chokes explained for them.
The story from Pentax is that the current engineers studied the drawings of a manual film winding mechanism and couldn't understand what certain parts were for, thought them unnecessary, and planned to remove them. The old engineers laughed at them and explained that those were among the most essential parts. And that once everything was explained to them, the current engineers then understood.
Of course, I am sure there were additional discussions and lessons that we have not heard about from Pentax.