What can be used as abbreviation for perpetual beta?

According to Wikipedia, we talk about stages of development;

• prealpha
• alpha
• beta
• release candidate
• stable

But, beta also have 2 sub-stages;

• perpetual beta
• open/closed beta

Now if we were to version a software with these and semver. It would look somewhat like this:

• prealpha: 0.x.x
• alpha: x.0.0-alpha.x
• beta: x.0.0-beta.x
• release candidate: x.0.0-rc.x
• stable: x.x.x

However how would these look if we want to differentiate between perpetual and open/closed beta?
Would this be allowed, and if yes would something like this work?

• perpetual beta: x.0.0-pb.x
• open/closed beta: x.0.0-ob.x, x.0.0-cb.x