The current standard used to create most types of digital certificates, no matter how they will be used, is to follow X509. A certificate made using this standard allows organizations the ability to easily share certificates between multiple applications, without compatibility issues. It also allows a business the ability to share certificates with other businesses, like their vendors or customers.
An X509 Certificate Can Have Different Versions
There can be different versions of an X509 certificate when organizations made modifications in-house. You can tell when there is a different version of this type of certificate because the X509 is followed by a period and a number. For example, X509.3 would tell you this was the third version of the certificate created by the organization. The reason organizations use different versions can be to keep track of different certificate types. They may decide they want to include other details within certain certificates, which is not required in others.