YOY - Prevent qv to substract year that has no value

[n1ef5ng1]

I have five year data, from 2008 - 2012

Bascially I am currently doing YOY on these data. I need to set Year_Month as my dimension as I need to extrapolate my latest incomplete month value.

Is there any codes that I am able to use to prevent 2008 to substract 2007 as there is no data at all?

One of the code is

=if( Before( Sum (IF(Derived_Status <> 'LRSHP', TEU,0)) )  = 0

  OR IsNull( Before( Sum (IF(Derived_Status <> 'LRSHP', TEU,0)) )) = -1, null(),

But i am unable to use this as Before will list out all the value in the dimension even if it is null or empty value.

This is my code for now

=(if( MonthEnd ( MAX( Date ) ) <> var_EndDate AND MonthEnd( MAX ( Date ) )
= MonthEnd( var_EndDate ) ,

(

  (sum({$<Year = {$(v_ThisYear)},Unlocode_Port_Of_Loading = {'ID*'}>} TEU))

-

  (sum({$<Year = {$(v_LastYear)},Unlocode_Port_Of_Loading = {'ID*'}>} TEU))
  / Day( var_EndDate )) * Day(MonthEnd(MAX ( Date )))
)
,

(

  (sum({$<Year = {$(v_ThisYear)},Unlocode_Port_Of_Loading = {'ID*'}>} TEU))

-

  (sum({$<Year = {$(v_LastYear)},Unlocode_Port_Of_Loading = {'ID*'}>} TEU))

)

))

Basicially the first line of code check whether is it the latest month, if it is, extrapolate the value.

Any help is appreciated as i m stuck for the whole day, thanks