Is it true that checking your credit score too often can harm your credit score?
No. Getting a copy of your credit report or your credit score does not go on your credit record.
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.)