Yes, applying for many new accounts can often damage your credit score more than applying for a single new account. There is no set number that is too many, but the fewer you apply for the better it is on your credit score.
Applying for one new credit card may have a small impact to your score, but applying for several can have a much more serious impact. It’s best to research the features and terms of each card and then only apply for the credit card that offers the features you want.
Your credit score presents a fairly accurate picture of your credit history, but not every account is recorded. Certain things, like your good history of rental and utilities payments are not listed on your credit report. Positive information from your landlord, cable, and cell phone providers is not reported to the credit bureaus.
No, in general credit scores do not change that much over time.
There are a variety of factors that impact changes to your credit score over time, such as: