Ok, I have some rows with blank dates in a "Date" column, yet I am still able to group by Month - per se in a PivotTable.

How is this possible? I thought that this wasn't allowed when it comes to grouping and that all cells/rows must have values to them. Apparently, this isn't the case with Excel 2010?

I tried earlier, and I wasn't able to, but I seem to be able to group by Date (Month) now with blank rows in the date field - I'm confused!

Thanks