This exact topic is covered in Wittgenstein's Philosophical Investigations, and the answer is that the concept of forest is not defined by such a condition. It is a basket of examples of forests and identifying a new example in the basket is done by means of analogy to the existing examples.

It is therefore possible for a concept to grow to include contradictory examples, at which point people will typically split the basket into two distinct concepts, like a forest vs a grove. The point at which that happens is somewhat arbitrary, but it also doesn't exist a priori. Someone has to try to use the word ambiguously. Words don't have meanings until they are used by people to mean.

It is even possible for a distinction to not be made, and for someone to experience cognitive dissonance when two contradictory examples remain in the same basket.

If you promise to chop down all forests but are fine with trees, yes.

Does this follow?

I run a site. I want to get rid of all fraudulent spam but allow legitimate commercial product advertisements. I train a model to tell the difference (or maybe I just make a human judgment call). It is better than guessing but worse than perfect: false positives and false negatives exist and expose me to criticism from interested parties.

Your position is that this renders the concept of spam meaningless because I promised to get rid of spam and allow non-spam content.

If you're tying ribbons to trees in forests but not to other trees, you (or other interested folks) can correct any errors. And, if you actually wanted to be fair, you'd fix your mistakes yourself (or with your own resources) instead of expecting everyone else to clean up after you.

If you have robots chopping down forests, there's not much to do when they're wrong except apologize and explain that algorithms are hard.