Value error in a multi-nested IF formula

EDIT: This wasn't the issue, so please ignore!


I've attached a worksheet which displays part of a large trade list. The purpose of the table is to give each trade an ID (separate from its ticket number).

The original formula in Column I is:

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Examples of this formula working properly are in rows 1 through 14 in the attached workbook. There's a bug which appears in F15. The value should be 25. But.. its 24.

So I've attempted a fix, here:

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But it doesn't work. Did I make a careless mistake in typing the formula, or the error due to another problem?

Thanks!