>To clarify, I have been tasked with writing an Excel worksheet parser, the input files can be xls or xlsx format. The data I require can be anywhere in the sheet but always has an identifier in column A where you start your import ( otherwise do nothing) , the minimum number of columns must be specified in advance.
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>An example usage from command line
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>Createcsv.exe excelfile.xlsx BT118
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>Where BT118 tells my program the identifier and number of columns to look for. I hope this helps.

If you can identify the start column maybe there's something in NPOI to get the 'block' of cells which you could then use to to write to the csv.
Update : Something based on this: http://stackoverflow.com/questions/21229203/read-excel-using-npoi-cell-range-address ?