Why is there a capital letter at the end of European patent number?

It is very important that the letters at the end of the patent number generally refer to the open type. For example, A refers to the disclosure of application documents, which does not mean that the patent must have been authorized, and B is disclosed after being examined and granted the patent right by the Patent Office. The public opinions of A and B may be different. Sometimes there is a number after the letter, such as A 1, B2, etc. This is similar in any country, not just Europe.