Re: I wonder if ...
On top of that - assuming they are still in the industry - they will have moved on to more modern electronics so may not actually be as well versed as the current team are anyway.
You seem to be assuming that moving on to more modern electronics means they don't remember the older stuff, but that is not the way it works (for me, at least).
I have been moving to 'more modern' electronics for decades but I can still remember the details of the (much) older stuff I worked on 50 years ago; the modern stuff builds upon the knowledge of the older stuff. There are newer methods of achieving the same results (software defined radio comes to mind) but doing a radio with purely analogue electronics is still perfectly achievable although there may be limitations (in both instances here).
I did my first multi-gigabit switch over 20 years ago; the underlying rules for that and more modern parts are the same but there are details that are not that important at lower speeds that can be major issues as the speeds become faster. These types of issues are not confined to modern processors - as an example, modern switching power supplies are a very different beast today although the functionality (from a top level perspective) is the same.
Layout has certainly changed over the years; what was appropriate in the 80s (with 70s and 80s era parts) is not appropriate for newer parts but that is because the newer parts have to be dealt with in context of their I/O speeds, not because the underlying physics has changed.
I currently work with very modern microcontrollers but I also work with a decades old radar system and I am quite comfortable with both.
It is perfectly possible that the original designers (and those who developed the various hacks over the years) have retired or even passed on but that is why documenting the design thoroughly (very likely more in depth for something designed in the 80s than present) is incredibly important.