(9.3 Beta 2) is not the same as (9.3.2). It's actually the same as (9.3.0 Beta 2).. Apple just does not ever use (x.x.0) they just shorten it to (x.x). (9.3.1) "could"be the version after (9.3) and (9.3.2) "could" be the version after (9.3.1). I say "could" because (9.4) will likely be released before (9.3) ever makes it that far.
The version hierarchy kind of works like this... (x.y.z). x = a major version, y = a notable change, z = bug fixes. The beta version is completely independent of that... Beta indicates the test stage of a version prior to being released. First it goes through "Alpha" testing. For example right now there is probably an IOS 10 Alpha 1.. Or where ever they are at on that... Alpha testing is internal company testing and the public never sees it... Then they move to "Beta" testing... Apple has developer betas and public betas....
Off topic but I doubt iOS 9 will see a 9.4. 9.3.1 for sure, maybe 9.3.2 but doubtful.
Going off last years timeline. 8.4 was released in April. 9.3 is said to be released this year in the "spring". Current rumours puts Apples March event on March 15. 9.3 will most likely be releasing pretty much same time to add support for the 5se and Air 3.
That leaves iOS 9.3 only a bit over a month "behind" in the timeline of where 8.4 was for release. That's not enough time to squeeze out a 9.4 and then a 9.4.1. It's really only enough time for them to do a 9.3.1 and maybe a 9.3.2
8.4.1 was in beta same time as 9.0 was. Same will probably happen again this year. The final version of iOS 9 will be in beta along side iOS 10 beta. They always leave an iOS version with a "z" update (as you labeled in the x, y, z above)
More off topic (and not arguing) I always thought of the (x, y, z) as x = version number, y = major update to that version (since these often offer something new or some changes) and finally z = minor update (nothing changes and just small bug fixes.)