Formula to calculate forwarded week of supply at the end to avoid the NA

I already have a formula to calculate the forwarded week of supply with match and index formulas. But at the end, there are not enough forward weeks of sales available, that is why I got NA as the result. To avoid this, I would like the formula to go back to the first week of sale (Cell C6 and on). See attachment Exercise 1.

On exercise 2, I would like to take the MD into considerations in the Forwarded Week of Supply.

Thanks for your help

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