Comparison Between Current with Previous Month

My table contains the individual month records that include Measure Date/Time, C-No, A-Set, Height-A/B, Thickness-A/B,

Gradient-A/B, P and R Date.

I would like to calculate and compare data between the current and the previous month, based on the following conditions:

1. When C-No and A-set match.
2. When C-No & A-set repeat within a single month, consider only the data from the most recent occurrence for the calculations. For instance, if the same C-No and A-set are recorded on both January 4th and January 20th, use only the data from January 20th for calculations.
3. Perform calculations (Height-A, Height-B, Thickness-A, Thickness-B, Gradient-A, and Gradient-B) current month's data minus the previous month's data, only if the P OR R-Date is falls outside the dates of the current and previous month, display "Nil." if no calculation is happened.

Refer to the attached files, the samples for both PB and Excel.

Sample Files 

Thanks for the help.