Countrows and filtering

Hi All

I have a dataset of former employees spread over 20 years with leaver reasons, I have a column created which flags whether the leave reason is voluntary or compulsory. I am trying to create a count which will count all voluntary leavers for the last 12 calendar months. The table is called 'Staff Data'.  Example data below.

In the example data I'd like result to be 4 (Retirement in May-21, Higher pay in Aug-21 and Oct-20, Conflict with manager in Jan-21).

I have a 'Date' table created and in this table I have create a measure (LTM Dates) which should flag only the last 12 months, using 2 other measures (StartDate and EndDate).

StartDate = EDATE(EOMONTH(today(),-1),-12)+1
EndDate = EOMONTH(today(),-1)

Using the above I have this measure:

LTM Dates = IF(MAX('Date'[Date])>= [StartDate]&&MAX('Date'[Date])<=[EndDate],true(),false())

In order to count the rows I need including I know I need to filter and this is what I've got so far but it's not working. It would be great if you could point out where I'm going wrong please.

CountVol.LeaverLTM = COUNTROWS(CALCULATETABLE('Date',FILTER('Date','Date'[LTM Dates]=TRUE),FILTER('Staff Data','Staff Data'[Vol. Leaver]= "yes")))

Thanks