'Year over year donor retention' only works with 'all gifts', and the filter of 'Revenue type' doesn't do anything to this report. There needs to be a way to exclude certain gift types such as 'pledges', and 'write offs' to show retained donors. By including 'all giving' you are including people that make pledges but never pay them. If anyone is currently using this report to show retained donors you will find that your counts are higher in NXT then any non-NXT reporting.