Really not sure if this is what you are after. (No sample results so i cant be sure)

;with cte2 as

(

select

[Invoice],

[D_Type],

[Status],

left(datename(month, [RemediationDate]), 3) as Mo,

year([RemediationDate]) as Yr

From

#Remediation

),

cte3 as (

select D_Type, Status, Yr, Mo, count(*) as #LineItems

from cte2

group by grouping sets

(

(D_Type, Yr, Mo),

(D_Type, Yr),

(Status, Yr, Mo),

(Status, Yr)

)

)

select *, AVG(#LineItems) over (partition by D_Type, yr, mo)

from cte3