Even if all of your lenders DO report to all three credit bureaus the information will probably be different – The lenders that do report to all three credit bureaus do so by sending data tapes to them each month. The problem is that the credit bureaus may not receive them at the same time and don’t “run” them at the same time. As such, your account information will generally be different depending on the time of the month.
It's rare that a free credit score truly has no strings attached. In the best-case scenario, you get added to the company's mailing list and have to manually unsubscribe if you don't want to be. Worst-case scenario, you enter your credit card and get automatically enrolled in credit monitoring services. This will show up as a recurring monthly charge on your credit card until you cancel it. However, there's usually a small window -- seven or 14 days -- after you get your free credit score in which you can cancel your subscription without being charged for credit monitoring.
Some of these reasons are relevant all the time; others matter most when you’re planning to apply for a loan. A mistake on your credit report could cost you thousands of dollars in interest over the life of a mortgage, for instance. So try to review your report as regularly as possible, but be extra thorough in the months leading up to a loan or credit card application.