The mIRC beta runs as an evaluation copy for me whereas all of my previous copies of mIRC used my registration (from the registry?)
Should it be detecting it or is it separate for now? And is the fact that I installed it as portable a problem for detecting registrations? If so, how does the portable version keep reg data?

It works for me. If you installed the beta "as a portable application" then it won't use the registry, which is where your registration is stored on normal mIRC installs.

When mIRC is installed as a portable application, it does not access/modify your registry in anyway and stores all data in the mirc.ini file where you installed mIRC.