Labels/Tags are a product feature, not part of email standards. Meaning: it’s not a thing when looking at the raw mail server data.

Thanks for the info. This helps me understand why things are the way that they are. It has me rethinking the use of tags altogether and leaning more toward reviewing my labels in gmail so I can tweak the ones that are still useful and remove any that are obsolete.

Agreed, this is where I’m at as well.

What I’ve had in place for the last decade or more made sense to me once upon a time, but it’s over engineered and of limited usefulness.

Despite the potential technical solutions offered in other comments, I’ve resolved to go through and clean up my email history, including deleting stuff I no longer need and reconfiguring how I assign labels to incoming messages in gmail in order to make sense to my current self and play nice with the folder system, which seems to be more industry standard anyway.