In our config profiles that are already set up, sometimes fields are checked in the PC column and sometimes a 1 appears in the # column.

What does each column do and why do I seem unable to place a number in the # column?

Against other fields that are not set to Ignore, the PC column is not checked, nor is there a number in the # column. Yet these fields would appear to be active.

Can someone help me to understand what is going on here please?

PC = Proper Case (replaces barbara daenzer with Barbara Daenzer)

The # column is for groupings. For example, if you are importing multiple attributes, all data related to one will have a "1" in that column...subsequent attributes would be grouped by other numbers.

Better examples at: https://omatic-importomatic.helpdocsonline.com/field-map

Fields set to Ignore are not being processed in your import, so having the PC column selected doesn't do anything

I also use the numbers for importing relationships, like when updating Solicitors and ending the relationship with one and adding a new relationship. Or if you are importing employees, spouse and kids, pets, etc.