Offset function giving a #N/A error when no data in the range

Hi

Please help to resolve my query.

I have data in a pivot with months as column headers and rows with client name. I need to determine
how many months since the last order. I am using the offset and match function to determine the last occurring value in a row but when a client has no orders for the months from Jan 14 until Mar 15 i.e (no pivot data), the offset function is giving me a #N/A error. How can i resolve this?

Formula =(MATCH(TEXT(Data!$K$2, "mmm-yy"),$B$4:$Y$4,0)-MATCH(LOOKUP(2,1/(OFFSET($B$4:$Y$4,MATCH(A8,$A$5:$A$930,0),)<>""),$B$4:$Y$4),$B$4:$Y$4,0))

B4:Y4 = Range of the pivot columns (months)
A5:A930 = Range of the pivot rows (Clients)

The Bold section of the formula is giving me the current Month position in the pivot.