How many replicas of custom image are needed if I don't need to create N scale sets concurrently?

Question

For Virtual Machine Scale Set deployments - For every scale set deployment with up to 600 instances, we recommend you keep at least one replica. For example, if you are creating 5 scale sets concurrently, each with 600 VM instances using the same image in a single region, we suggest you keep at least 5 replicas of your image.

According to the official doc above, if we create N scale sets concurrently, we need to keep at least N replicas of my image. But if we don't need to create N scale sets concurrently (because the creation is on-demand), is it still necessary to keep N+ replicas for these N scale sets? For example, here is the telemetry about how many scale sets are created by the time. Should we create 2 scale sets for this region? or just ONE is enough because no concurrent creation.

timestamp | # of creation
07:01:07 | 1
07:01:16 | 1
07:01:26 | 1
07:01:29 | 1
07:01:37 | 2 ---> created at 07:01:37.385 and 07:01:37.623
07:01:41 | 2 ---> created at 07:01:41.842 and 07:41:37.958
07:01:48 | 1
07:01:52 | 1
07:01:59 | 1