The KV-1 cannot penetrate a Panthers front armor (hull or turret) at 500 meters. Not with a 76L/41 gun. You would need a side hull or side turret hit, or a rear hit to knock it out. Its "possible" that a round hitting the front of the Panther will "shot trap" off the turret and go through the top hull, that happened, but it would be a lucky hit...
The KV-1 was a shock to the Germans, as was the T-34, in 1941-42, but the Tiger I and Panther were several steps up in class by the time they were deployed in late 1943.
You need a KV-85 or a T-34/85 with an 85mm gun to try and win a fight vs a Panther, and even at that, you would want tungsten shot (APCR).
All that being said the MkIV series was vulnerable to T-34s and KVs, and they made up the majority of the Panzer forces.
To face a KV-1 M1942 in 1942 with a MkIII or a MKIV you were in for a fight if they were a good crew, it was probably the most formidable tank in the word at that time.