I'm not sure about the details. Having your credit checked too often is a minor negative (i.e. It makes it look like you are about to add lots of debt.) Unsolicited checks of your credit (by credit card companies with pre-approved offers) does not impact your credit. I don't know about personally checking your credit.
I have the three companies set on my calendar 4 months apart. I check each one once per year. (Not a score, but only credit history.)
I've had my credit union tell me my score before. I'm not sure what their policies or rules are. (i.e. I'm considering refinancing, what does it look like? What kind of rate will you give me? Etc.)
Just an FYI, the only people who are supposed to provide your score is the credit bureaus. The car dealer or credit union or bank are not supposed to give you the actual number. They usually will if you ask nice.