Since the table already contains the previous year's YTD totals, would a simple LEFT JOIN suffice to get the prior year's YTD total?
SELECT
t1curr.cod, t1curr.[year], t1curr.[month], t1curr.value, t1prev.value
FROM dbo.Table_1 t1curr
LEFT OUTER JOIN dbo.Table_1 t1prev ON
t1prev.cod = t1curr.cod AND
t1prev.[year] = t1curr.[year] - 1 AND
t1prev.[month] = t1curr.[month]
SQL DBA,SQL Server MVP(07, 08, 09) "It's a dog-eat-dog world, and I'm wearing Milk-Bone underwear." "Norm", on "Cheers". Also from "Cheers", from "Carla": "You need to know 3 things about Tortelli men: Tortelli men draw women like flies; Tortelli men treat women like flies; Tortelli men's brains are in their flies".