First question - I've seen several other threads about submitting CPE hours for the self-study that resulted in a passed certification exam, and in each it is mentioned that you can claim up to 30 CPE hours. For instance:
However, I cannot find any official reference to this in the current CPE Handbook or FAQ:
Is that information still accurate? Is it documented anywhere?
Second question - I recently received notification that I passed the CompTIA Linux+ certification exam. This is not a security-specific exam; however, the study material was technical and covered many security-related topics. Would this be Class A or Class B CPE?
As I stated in one of the threads you've linked in your post, you earn the CPEs for the studying not for taking the exam. So it shouldn't matter if you pass or fail, or even if you take or don't take the exam, you can still earn the CPEs if you did the study:
"Group A and Group B CPE Credits
Self-study related to research for a project or preparing for a certification examination."
As to the amount of CPEs you can earn being up to 30, this has been stated numerous times on this forum by members of ISC2 staff, so that's good enough for me. One of those threads you have linked is only 4 weeks old so the advice should still be accurate. I have claimed CPEs for 2 periods of study relating to certifications so far (60 CPEs total) and intend to do more.
I haven't seen the amount (up to 30) documented anywhere other than here, or any information on how the amount was arrived at. The amount still follows the usual calculation of 30 CPEs equals 30 hours of study. This was fine for my CCSP as I did just over 30 hours of study. However, for my ISSEP I did over 80 hours but only claimed for 30, and by the time I take the ISSAP exam I will have done close to 100 hours of study, so to me the number 30 seems kind of arbitrary. I think they should just stick to the usual 1 hour = 1 CPE and not put limits on things.
(I know I could potentially claim the additional CPEs beyond the 30 for my ISSAP/ISSEP studies by submitting the remainder as book reviews or something else appropriate but I don't struggle for CPEs so can't be bothered - and don't want to take the risk of being accused of breaching the code of ethics!)
In terms of your question about your Linux+ certification, when you submit CPEs you have to submit them against which domain(s) of your ISC2 certification they cover. I'd look at the CISSP domains and see where you think the CPEs for your Linux+ study might fit. If they don't fit any of the domains then they're group B. Given your time was spent studying security and non-security related topics I would split them between group A and B accordingly.