Hi Phil and welcome to the forum,
Everytime you create a new Pivot Table and put it on a sheet, it gets a number. That number is normally one bigger than the last pivot table you put on that sheet. It sounds like you have put 11 previous pivots on this sheet as you are up to number 12. If you remove a pivot table on a sheet or delete the columns it is in, I believe this will really remove it and start counting over.
The way to test this theory is to go to the VBA editor and in the immediate window type:
debug.print Activesheet.PivotTables.Count
and press enter. The number of Pivot Tables on the current sheet will be displayed.
Then type
Debug.Print ActiveSheet.PivotTables(1).Name
and press enter. This will display the name of the first pivot table on your sheet. If you have more than 1 then change the 1 to a 2 and get the name of the second one.
I'm not sure what your actual question is in this post but here are some things to try.
I've created a Named Range for my data and use this name when dealing with Pivot Tables. When I create a Pivot Table or Pivot Chart, I use this Name instead of the Absolute range of cells. This might solve your problem
If your data grows or contracts then I'd use a Dynamic Named Range whoes name would be used as the data source for you Pivot Table.
See http://www.ozgrid.com/Excel/DynamicRanges.htm for some examples
hope this helps.
Bookmarks