Improved Excel source
Excel reader does not handle Excel dates well. Use the DateUtils.isDate in POI library (or something like that) and read the Date value (getDateValue()) of the cell and return the value formatted as YYYYMMDD.
This should work for preview and actual sending of data to server.
Blank cells at start of row
It appears that Excel reader strips out the first cells if they are blank. This should not happen.