Difference between current and prior period

[NewbieToQV]

Hi, I need to generate a output that compare current period to previous period. Appreciate the help as it quite complex for me.

Data:

Result:

 

tab1:
CrossTable(Month, Grade)
LOAD * INLINE [
ID, 1/1/23, 2/1/23, 3/1/23, 4/1/23, 5/1/23, 6/1/23, 7/1/23, 8/1/23
1000, , , A, B, A, , ,
1001, , , , , , , D,
1002, , , , , , D, , A
1003, A, B, B, , , , ,
];