What would happen if blood flow did not increase before the exoskeleton hardened?

The animal would not be able to grow effectively. Increased blood flow makes the animal swell up, making the hardening exoskeleton slightly larger as well. If the exoskeleton was never expanded in the first place, I'd imagine the arthropod would be stuck in a small, static shape.

this is a good question! i'll do some research and come back when i have the answer!