You do not really seem interested in what we have to say, or whether or not we agree with you. You have merely stated your inflexible position for others to see. Regardless of that, here is my supporting evidence and opinion.
PC's do not spend the 16 - 100 years prior to starting their adventuring career in a vacuum. One can only assume that during this time they learn a bit about the world around them.
Most primitive cultures, and I think that the large majority of D&D cultures could be classified as primitive, develop and cultivate a vast amount of information about the world around them.
They know what plants and animals are dangerous, and they learn how to deal with, and limit, those dangers. Their continued survival depends upon this.
They learn which plants and animals are edible, and what methods are most effective in hunting or gathering those foods. Again, their continued survival depends upon this.
To propose that a population lives in ignorance of those dangers that exist within their proximity is absurd. Any such population would be decimated in a very short period of time. If that is one of the planned occurances for your campaign, great, otherwise, your reasoning is flawed.
Your position, that because the PC's are low level they know next to nothing about the world in which they live in is ridiculous. Any being that could not learn to recognize the dangers around itself would die early in life and not make it to adulthood.
The behaviors, habits, and physical description of every creature listed as 'common' in the MM, that lived within the geographic region where the PC's grew up, would be generally known. This information would pass from generation to generation as a survival mechanism.
You could argue that the general populous of the more civilized areas would have less knowledge of these creatures, but much as children in our generally civilized and urban world generally know about lions, elephants, snakes, tigers, bears, and other dangerous creatures, these people would have more 'second hand' knowledge of those 'common' creatures in the MM due to the availability of books and other sources of information.
In the same vein, just as we would know not to hunt an elephant or rhinocerous with a slingshot or wooden club, low level PC's would know not to hunt creatures 'common' to them with weapons that were ineffective. If were-creatures were 'common' to the area where the PC's grew up, or 'common' in general, they would know that silver weapons were required to harm them. Any position to the contrary would be unsupportable.
As a player, I would not trust a DM who changed the game rules without letting me know in advance. I expect to play D&D using the D&D rules, unless the DM tells me differently. It is common courtesy to let people know that you are changing the rules to a game, whether that game is D&D or Monopoly.
As a DM, I would respect my players enough to let them know, in advance, about any game rules that I was going to change. I would also trust them to keep this knowledge seperate from the actions that their characters take. If there was obvious overlap I would discuss it with the player. It's really that simple.
Obviously I am not going to tell them about changes to creatures, as that would serve no good purpose, but the game rules are there to set the playing field, and that playing field should be visible to everyone.
I'm don't know you and am not accusing you of this, but I've seen DM's act in a manner similar to yours in the past, and it has always ended up being an ego or power trip issue. They were serving some need for control that they had, at the players expense, and it always ended the game prematurely. Stuff like this isn't 'fun' or 'cool' for the players, it is frustrating at best, and downright infuriating at worst.
Reading your replies really reinforces, in my mind, the idea that you do not have any respect or trust for you players. If your game has really reached such an abysmal level, why do you continue?