If you define "not still in a beta state" as no longer in development, then probably yes.
Technically, every software item ever released is in "a beta state" even if not labelled "beta". Because
when new bugs are found, not
if they are found (no such thing as "bug free" software), then a fix will usually, eventually, be released until the next bug is found (in either the "fix" itself or in the original software) ... and the process continues in an endless cycle for as long as that software is continuing to evolve and updates are released. This is the software maintenance cycle and continues until someone decides to stop development and support of that particular release. After that, no more bug fixes.
My copy of Trainz Plus build 134634 is a beta version. How do I know this: It is in the
Trainz Plus Beta Update Stream - look in Trainz Settings -> Install -> Change Trainz Update Stream.... To remind me of this, every time I launch it the letters "Beta Stream" in big, bold, white appear on the bottom right of the launcher - I added that to the background graphic myself. Every time I discover a bug I report it - it is part of being a beta tester.
My copy of Trainz Plus build 132284 is
not in the Trainz Plus Beta Update Stream so it is, allowing for my statement at the start of the second paragraph above, a retail release. It still has bugs as does all software and these bugs, if you discover any, should be reported via the
Bug Reporting Page.
When I signed up for the Trainz Plus subscription, I was fully aware of the status of its new features as "experimental" (code for probably "buggy") and I accepted that. I also accepted that Trainz Plus is a work in progress, with new features that will appear (e.g. TLR, Multiplayer Surveyor, etc) that are not yet in a full operating mode.
TANE, TRS19 and TRS22 are more like "fixed" products in that they will probably not receive updates with major new features. They will certainly receive bug fixes and probably some "housekeeping" changes.
Apart from the subscription side of things, Trainz Plus is not for everyone. I, on the other hand, am quite satisfied with Trainz Plus, both the beta and non-beta versions, and will continue the subscription.