Hi Kiran,
When you have specifically allocated 100 each for SA1, SA2 and SA3 the there is no way system is going to allocate remaining allocation at product location level for SA1 after you consume assigned quantity of 100 to SA1.
With your requirement i am unable to make out any business sense, as in this case entire quantity is to be made available to each of the sales org., which is similar to the situation where there is no allocation.
Can you please explain the business logic behind this requirement, to make my understanding clear, and also to facilitate my thinking process in required direction.
Rgds
Sourabh