Some more sample data would probably make sense. Have a play with this and see how you get on:

-- Amended function

ALTER FUNCTION [dbo].[IF_Calendar] (@Enddate DATE)

RETURNS TABLE AS RETURN

WITH

e1 AS (SELECT d.n FROM (VALUES (0),(0),(0),(0),(0),(0),(0),(0),(0),(0)) d (n)),

e2 AS (SELECT a.n FROM e1 a, e1 b),

iTally AS (SELECT n = -1+ROW_NUMBER() OVER(ORDER BY (SELECT NULL))FROM e2 a, e2 b)

SELECT TheDate, [DayName],

DayNo = 1+(DATEPART(dw, TheDate)+@@DATEFIRST-2)%7,

WeekNo = ROW_NUMBER() OVER(PARTITION BY YEAR(TheDate), MONTH(TheDate), [DayName] ORDER BY TheDate)

FROM ( -- f

SELECT TheDate, [DayName] = DATENAME(WEEKDAY,TheDate)

FROM ( -- e

SELECT TheDate = CAST(DATEADD(day,n,Startdate) AS DATE)

FROM ( -- d

SELECT

Startdate = DATEADD(YEAR,-2,DATEADD(MONTH,DATEDIFF(MONTH,0,@Enddate),0)),

Enddate = CAST(@Enddate AS DATE)

) d

CROSS APPLY (SELECT TOP(1+DATEDIFF(day,Startdate,Enddate)) n FROM iTally) x

) e

) f

GO

-- Amended query

;WITH MyData AS (SELECT * FROM (VALUES

('2012-11-12', 'DM1', 'Monday', 750),

('2012-11-12', 'DM4', 'Monday', 76),

('2012-11-12', 'DM5', 'Monday', 501),

('2012-11-13', 'DM1', 'Tuesday', 110),

('2012-11-13', 'DM4', 'Tuesday', 476),

('2012-11-13', 'DM5', 'Tuesday', 1501),

('2012-11-29', 'DM1', 'Thursday', 110),

('2012-11-29', 'DM4', 'Thursday', 476),

('2012-11-29', 'DM5', 'Thursday', 1501),

('2013-11-11', 'DM1', 'Monday', 1542),

('2013-11-11', 'DM4', 'Monday', 12),

('2013-11-11', 'DM2', 'Monday', 235),

('2013-11-12', 'DM1', 'Tuesday', 152),

('2013-11-12', 'DM3', 'Tuesday', 1214),

('2013-11-12', 'DM5', 'Tuesday', 2035),

('2013-11-28', 'DM1', 'Thursday', 1521),

('2013-11-28', 'DM3', 'Thursday', 4021),

('2013-11-28', 'DM4', 'Thursday', 25),

('2012-12-03','DM1','Monday',441),

('2012-12-03','DM3','Monday',10),

('2012-12-10','DM4','Monday',25),

('2013-12-02','DM1','Monday',1521),

('2013-12-03','DM4','Monday',4021),

('2013-12-03','DM4','Monday',25),

('2014-12-03','DM1','Thursday',1521),

('2014-12-03','DM3','Thursday',4021),

('2014-12-03','DM4','Thursday',25)

) d ([Date], Stack, [DayName], ParcelCount)

)

SELECT

[Month] = DATENAME(MONTH,c.TheDate),

m.Stack,

c.WeekNo,

c.[DayName],

ParcelCount2012 = SUM(CASE WHEN YEAR(c.TheDate) = 2012 THEN m.ParcelCount ELSE 0 END),

ParcelCount2013 = SUM(CASE WHEN YEAR(c.TheDate) = 2013 THEN m.ParcelCount ELSE 0 END),

ParcelCount2014 = SUM(CASE WHEN YEAR(c.TheDate) = 2014 THEN m.ParcelCount ELSE 0 END)

FROM [dbo].[IF_Calendar] (GETDATE()) c

inner JOIN MyData m

ON m.[Date] = c.TheDate

WHERE MONTH(c.TheDate) IN (11,12)

GROUP BY

MONTH(c.TheDate),

DATENAME(MONTH,c.TheDate),

c.WeekNo,

c.DayNo,

c.[DayName],

m.Stack

ORDER BY

MONTH(c.TheDate),

c.WeekNo,

c.DayNo,

c.[DayName],

m.Stack