When filtering the Cost Summary Pulse report to just the EDP Credit charge type, the "Last Month at This Time" figure is the same as the "Last Month Total Cost" number.
This is working as designed.
For the EDP Credit charge type calculation the credits are accounted for on the first day of the month. This causes the “last month at this time” figure to always equal the total for the whole month. Other reports will break this data down to a daily granularity, but that is not the case with the Cost Summary Pulse figures.