declare @d date = getdate();

with T as (
	select 2021.0 as [Год], 12.0 as [Месяц]
),
d as (
	select dateadd(month, -1, @d) as d
	union all
	select dateadd(month, -2, @d)
	union all
	select dateadd(month, -3, @d)
)
select	T.*
from	d join T on
	T.[Год] = year(d.d) and
	T.[Месяц] = month(d.d)
;