Another way, if the functions in the freely downloadable file at
http://home.pacbell.net/beban are available to your workbook:

=VLookups(1234,A1:B100,2) array entered into a column of cells
sufficient to accommodate the number of occurrences.

Alan Beban

Peo Sjoblom wrote:
One possible way

=INDEX('another sheet'!$B$1:$B$100,SMALL(IF('another
sheet'!$A$1:$A$100=$B$1,ROW('another sheet'!$A$1:$A$100)),ROW(1:1)))

where B1 holds the serial number to lookup, A1:A100 the serial numbers
and B1:B100 the dates

enter with ctrl + shift & enter

copy down until you get an error