First, Apache will always use base64, file extensions are irrelevant (pem,crt,cer).
Second, you cannot issue a certificate for longer than the certificate authority.
10 years is a bit much, I wouldn’t be surprised to see browsers begin to mark them as insecure.
If you still have the issued certs, you can validate them with openssl.
https://security.stackexchange.com/a/56699/84379