If/Then Data Comparison

Im at work doing the same tedious work over and over for 18k+ entries and i know excel can do this work for me. here's what i have set up:

ּ ּ ּ ּ A ּ ּ ּ ּ ּ ּ B ּ ּ ּ ּ ּ ּ C
01. 101-A.......101-A.......-------.....
02. 102-A.......103-B.......Error.....
03. 103-A.......106-A.......-------.....
04. 104-A.......107-A.......-------.....
05. 105-A.......109-2........Error.....
06. 106-A.......113-1........Error.....
07. 107-A.......115-A.......-------.....
08. 109-A.....--------
09. 110-A.....--------
10. 112-B.....--------
11. 113-B.....--------
12. 115-A.....--------

I need column C to tell me what the discrepancy between column A and B if there is one at all. I have a formula in column C to tell me that they don't match, but i don't know how to to make it pull any information from the other cells:
=IF(B2=0,"",IF(COUNTIF(A:A,B2),"",IF(ISERROR(FIND(LEFT(B2,3)*A:A,2))=TRUE,"Error","")))

NOTE: this is an extremely simplified example; my document has far more numbers, mixed with some letters in each field. Macro's are also not an option unfortunately. Aligning column B to column A also isn't an option because there are some fields in column B that just don't exist in Column A