- A reference guide and manual in Russian for Heroes 3.

if as a result of RND the Knight's damage was determined to be 20, then in the event that luck triggers he will deal 40 damage, and if double damage also triggers - 60.

With very high probability, it will work exactly like that. The only caveat is that to verify this in practice (I haven't checked), one would need to find a way to bypass the limitation of the Knight's base damage range of 15-30.

Or approach it from the opposite direction - if, in the case of luck and double damage triggering simultaneously, the resulting damage is odd even once, one can safely assert that these parameters are not multiplied, meaning the theory proposed above is correct. But for verification, you would need either a lot of time or a lot of luck to wait for such an outcome... :)