If everyone acts like an adult, these become non issues.
I don't agree with the "don't ever say anything" advice. I DM probably 75% of the time, and I am not always right on a rule. My players know that if there's a potential mistake, to let me know right away. The key again goes back to how you handle it. If everyone acts like an adult, these become non issues. In this case the answer might be "Oh, you're right. My bad" to "Yeah, but they seemed nerfed to me like that, so I changed it up to fit the adventure better." Either way, you move on
I wouldn't mind if a player said something like "Isn't that ability limited to 30 feet?". As a DM, I do mess up on occasion and have no problem admitting a mistake.
If I have modified a monster for one reason or another, my response may be "Normally yes, but this one seems to be able to reach 70 feet."
If a player continuously questions my actions as a DM, that is a separate issue which would be dealt with as appropriate.