Something that has been on my mind is that we've never addressed where those chicks are coming from. No problem with days olds, but I'd worry about anything over 5 weeks being introduced. Shouldn't they be quarantined if they come from another flock or even a hatchery?
Yes, 100% always quarantine. You can get lucky 99 times out of 100 but it only takes once to introduce an infectious disease into your flock. I have had personal experience with this (MG and MS infections due to poor quarantine procedure) and believe me, it's heartbreak whether you choose to depopulate or keep the birds and treat whatever ones you can.
The only exception I ever have to quarantine is chicks >1 week old, originating from an NPIP hatchery. Any chicks who come from non-NPIP breeders and any juveniles/adults should ALWAYS be quarantined. You are so, so much better off safe than sorry.