Do you not find that there is never a perfect repair in the SRM. You always have to make your own variation from the ideal.
Even if you only vary the rivet pitch!
I think that we make that decision to vary on experience and common sense. If we had to go to the manufacturer each time the land or pitch differs from their drawing then we would be there all day.(and night)
The SRM is the ideal, same as the MM. If we get somewhere near that ideal then surly that is good enough.
It may sound daft but the lowest acceptable standard is good enough.
We are not after new aeroplanes...only serviceable ones!!!