consecutive 3 batches is not a standard figure. The main purpose we need to prove the consistency and reliability on our process. So 3 is considering as a minimum to show the consistency.
When we choosing the batches it should be normally on starting batches (1, 2 & 3). If we using the process pathway & components are dedicated to that product then we can use some rational to mitigate why (4,5,6) other batches were used and acceptable. If that is not the case then it is very difficult to mitigate. You need to hold all the batches that were manufactured in between until proven your process is meeting the acceptance criteria.
It is mainly risk taking factor for time. you can complete 3 batches on same time and wait for results. in this case if you got any failures you need to complete corrective actions and repeat the whole exercise again. If you have the time and wait for each batch results then you can save the time and cost by implementing your actions prior to start your next batch.