A little history, for those not in the know: The original laser pistol props were used in the two pilot episodes (with modifications in the second). The black and white hero phasers were built when the series proper went into production. The P1 first appeared in “The Corbomite Maneuver”. The P2s first appeared in “The Enemy Within”. The vacuformed crapazoids were built as dummies.
After the inital batch of episodes, the phasers were repainted and reworked into the versions we know now. The first appearance of the revised props was in “Dagger of The Mind”.
By the end of the first season, it was determined that higher-quality dummy phasers were needed, and so the midgrades were built, with “The Devil In The Dark” being their first appearance.