Look at the data ... XSLX is a Zip-compressed XML file, if I recall correctly. Don't try to guess by "looking through a glass, darkly." Go to the actual source and see what is actually there. It's quite likely that what Excel put there is its internal representation of a date, which would be "days since some epoch."
Comment on Re: Spreadsheet::XLSX date format problem
"Source file value : 10/23/2013
The actual data once parsed : 41570 ( The values returned from the cell while reading the data from that cell).Source file value : 10/23/2013
The actual data once parsed : 41570 ( The values returned from the cell while reading the data from that cell)."