Compare two dates and possibly third if it exists to confirm <30 days

Hello. I've been trying to figure out a formula to compare three dates, when at times all three are not always present.

#1 - initial
#2 - secondary
#3 - final

There is always an initial and a final and the number of days between needs to be 30 or less. If there is a secondary date present, then the calculation needs to work from the final to the secondary to determine if the number of days is 30 or less. If there isn't a secondary date present that field will contain "N/A".

I've added extra columns and did summary calculations
final - initial = D3
final - secondary = E3

and then wrote the below, but that doesn't include situations when the secondary doesn't exist. It also adds extra columns to the spreadsheet which is undesirable.

=IF(D3>E3,IF(E3>30,"Late","ok"))