What are your thoughts on the usefulness of tribal knowledge when older (age-wise) employees change jobs? [0]

Then, the tribal knowledge they had at their previous place of employment won't be as useful somewhere else. Though I suppose you can make an argument that they might have similar workflows, or tools, or they might just have general experience that would be useful.

But I suppose your comment was more on the under-appreciation by management of existing tribal knowledge in a team.

[0] Perhaps out of necessity, e.g: company went under, or maybe they want a change of pace.