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Ah, ok, that's much better information. So, your column C shows the last 20 entries in column A?

Now I see the problem. Your long formula construct is designed to spot the last 20 "text strings" in column A, but the last few entries you put in column A are not text, they are real numbers. Notice the little green flags in that column? That's to warn you that your values are not the same "type", or are text that appear to be numbers but are not.

So, the first thing to do is correct the column so that all values are the same type. I would personally convert all the values to true numbers and apply a custom number format of 000 to show the three-digit display as you have.

Or, you can convert the new entries at the bottom to text by added an apostrophe to the start of the numbers, that would allow you to keep using your long formula construct.

But we can accomplish the same thing with a much shorter formula. In the attached workbook you see the formula for true numeric values in C1, copied down. You also see the formula for all text values in G1 (looking at column E), and also copied down:

=INDEX(A:A, MATCH(99^99,A:A, 1)-19+(ROW(A1)-1))

Put this in C1 and copy down: