I'm not quite sure what it is you are counting. If you have the same start and end date, the implication is that, actually, you have a count of 1.

However, if you have, say, 13, start: September and end: 14, September, would you count that as 1 or 2? If you just subtract the dates, you get 1. But, based on the logic for start and end dates the same, that would be 2.

If that logic is correct for what you want, always add 1 when you subtract the two dates.

See your first entry:

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Regards, TMS