Yes, certainly I meant 2.18 instead of 2.19. Only where I meantioned 184.108.40.206 I could mean that or better 2.18.1 Beta, however now I think once Alpha is released, so 2.18 you should wait 2 weeks to release fixes so 2.18.1, and when there's need after another 2 weeks 2.18.2, what most possibly would be the last vers. before starting 2.19 Beta.
Good idea to force users to be Beta testers, but on the condition you won't give more than 3 new features per one minor release. After 2 weeks make fixes if needed, and when during next few weeks nothing was reported then release another 2-4 features (and so on), so like the first would be 2.19 (then if corrected 2.19.1), and then 2.19.2 (2.19.1 if not fixes were required after first update). You could also keep 2.19.1 (2, ...) for regular alphas, while between them something like 220.127.116.11 (2, 3, ..) for fixing bugs (however 18.104.22.168 probably would be first and the last, while 22.214.171.124 maybe needed only sometimes). That could be then also named 2.19.1b (c, d, ...), while regular 2.19.1 (with new features only) would be 2.19.1a by default but with not displayed a letter. Of course the 4th number after 3rd dot could not work accordingly to that you said.
That would change probably Beta period for 2.19 as that would be released with Alpha is, by turns. So you could release 2.19 Beta in first instance up to 126.96.36.199 (however you only used no more than 188.8.131.52 for another beta updates), and then all collected ideas realease in 2.19 (alpha). The same for another Beta so 2.19.1 up to 184.108.40.206 to finish by 2.19.1 (alpha). For now there was only Beta before you shared alpha, so this system should look like it.
I like your idea because that's true majority of users don't participate in Beta's, and I'm sure you won't be like Adobe which doesn't respect users. For the whole year from Alpha (that is in last years simply Beta!) they fix bugs they introduced together with new features, but not all, something like 70%, while they let live the rest of them. So if you followed your way and fixed fully everything right after that was released then your users wouldn't like those of Adobe products revert to previous full Alpha version while next one already is up from a yaer, but going finally to that another version (with plenty of fixes) when even newest got eventually released as well (again buggy that noone wants to use it).
Why you have to wait so long to get certificate, can't you ask of it a month before expiration, so you can have it when current one is about to be expired. Probably not - as you had to have parrarel version that would then turn into regular one