I called Apple for a separate account question I had so I asked about this at the same time. I asked Brian (Senior Advisor from Apple Developer Program Support) to email it to me so it's official. There are no public facing documents for this and because of that Brian actually submitted this information to Apple as feedback so in the future it is something we would be able to reference online.
Officially from Apple Developer Program
Conversation and official email
A maximum of 3 app store and Ad Hoc production certificates can be active at the same time for the Apple Developer program. For Enterprise it’s 2 certificates.
If you want to verify the limits for certificates the best option would be to visit the Certificates, Identifies and Profiles Portal and create additional certificates. Once the option is grayed out, that will indicate that you have reached the limit of certificates that can be active at one time.
Two Enterprise Distribution certificates can be created at a time and a single Enterprise Distribution certificate can apply to several apps.
Each Enterprise license is completely distinct with independent distribution certificates. If a company registers in five Enterprise programs they will be able to create five independent distribution certificates.
However you can create or revoke them as frequently as you’d like.
Instead of having multiple certificates, you can export the same certificate and use on multiple workstations
