Cleon
Legend
I suspect the latter - Mike Shea talks about this often (official dnd monsters doing too low damage for their CR) - but clearly some are the other way. Maybe they rushed them...who knows
The CR Calculator does seem broken though. It gives the same adjustment for immunities as it does resistances: +100% effective hit points for both. If I remember correctly it's supposed to be +50% for resistances, +100% for immunities.
Not that it matters in this case, since a Lycanthrope has damage immunity.
Anyhow, so are we using the Calculator DPR of 15 to 32?
That'd make the Weresnake a bit of a glass cannon, but the original kind of was since it had a save-or-die venom and not that many hit points.
The maximum physical DPR is 6½ slashing (scimitar) plus 5½ piercing (bite) for 12 damage, meaning its poison can do anywhere from 3 to 20 damage according to the Calculator.