1907 Liberty V Nickel Error Type

Doesn't look like an error to me, I'd say it's PMD, or POST Mint Damage.

Also, ! Keep the questions coming!

Welcome to Coin Community, melneb. The most important knowledge regarding errors is knowing what can and cannot happen at the Mint during the die preparation process and the strike. The feature seen here is simply not possible from the Mint - they have no way of messing up a strike in this fasion because it would have had to involve all 3 components touching the planchet during the strike, both dies and the collar. There just isn't a failure mode which would allow something looking like this. It's basically knowledge which can only be gained by experience.

With that as a given, the obvious cause here would have to involve a pinching tool of some sort.