Fixing moderate fret wear?

[grobe]

Is this what "crowning and polishing" is? Never understood what terms are what. Is this a good thing to do before the wear becomes excessive and therefore problematic? I don't think the bass in question is there yet.

[Turnaround]

Strictly speaking, crowning and polishing are the steps that happen after levelling. If there is a divot worn into a fret, crowning is not going to fix it on its own. You need to file the fret down until you have a flat surface across the whole fret (albeit a very narrow flat), then recrown to round the top surface again, then polish until nice and smooth and shiny-like.

Levelling, crowning and polishing are not preventive measures, they are corrective ones. So there's no reason to do any of these unless there is sufficient wear to warrant it.

[grobe]

Can I assume the leveling/crowning should only been done once? After that it's brand new frets?

[Turnaround]

Levelling and crowning can be done multiple times depending on the size of the fret and the amount of wear. Once the fret gets too low to crown properly, it's time to replace them.