Hi Imran,
I wonder is it really the correct thing to exclude a week of your sales?
Do you want to compare week 10 this year V's week 10 last year - if so you can change your offset to -53 instead of -52.
We use a lot of Customer Exits on time, and where we derive MTD values, we make allowances in the code for 53 week years. Typically we add the extra week into August (different companies will make different decisions) so in August for last year our week numbers would be 31-34 and this year would be 31-35. Sept last year would be 35-39 and this year 36-40 and so on.
With regards
Gill