I have a worksheet that has in column A a unique identifier. And then
for each of those idenitifers, an X in a column under a month.

    A    B    C    D

1        Nov    Dec    Jan
2    15        X
3    11    X
4    12            X
5    10        X
6    14            X
7    16    X
8    13        X

Then in a seperate worksheet in column A i have those same unique
identifiers as above.
I want column B to list the "Month" column that that identifier appears
in.

Basically a formula that looks finds the corresponding unique ID in the
above worksheer, finds the X in the same row, and then outputs the
date.

    A    B

1    10    Dec
2    11    Nov
3    12    Jan
4    13    Dec
5    14    Jan
6    15    Dec
7    16    Nov

Ie so in the above, Column B would be a formula that outputs the either
the contents of B1, C1, D1 from the first worksheet (ie the date
specified there), depending on where the X is.

Hope this makes sense!

Any help woudl be greatly appreciated!