Mark,

The below article from Sweetwater explains Nashville notation pretty well.

https://www.sweetwater.com/insync/the-nashville-number-system-demystified/

It seems that both ways are legitimate (examples 2 and 3). That said, using the relative major for chord notation is the recommended approach. BIAB does both. There is a option in Display Settings called "For Roman numerals of chords in minor keys, use the relative major". This setting also works with the Nashville system.

Hope this helps,
--Noel


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