Dynamic Pivot Table changing the SourceData

I have a manually created pivot table on a sheet and have VB code that rebuilds that pivot table, basically changing fields based on certian selections. Now when I run the macro, the SourceData changes from having 40,000 rows, to 13717 rows. If I don't specify the sourceData, will Excel default to a set number of rows? What other reason would cause this? If you need the source code, please let me know.

Thanks for any help you may offer
-Rich

I figured out the issue, I was using a reference pivot table that had the number of rows used for the source data.

Thanks
-Rich