Today's new Flash Player Beta files are outdated(old files still are v26.0.0.123)!

Actually, that's a little ambiguous:

In this instance, we did release a new build outside the regular release cycle, which fixed a functional bug (26.0.0.131).  Since there's not a security issue addressed by 26.0.0.131, there's no new security bulletin mentioning it.  At that point in time, , if you were on 26.0.0.126 or higher, you were good from a security perspective.

We've released again since then on the regular monthly cadence (26.0.0.137), which is the current build.

I think you're conflating the purposes of these things.  The security bulletin exists to let you know that we've identified and corrected a defect that has security implications.  (We don't differentiate between theoretically and actually exploitable, either.)

Because we invest heavily in proactive security work, it's pretty common for the latest bulletin to point to the latest Flash Player, but technically, that's not it's purpose.  It points to the last version of Flash Player that has a security fix that you should take.

In this instance, we did release a new build outside the regular release cycle, which fixed a functional bug.  Since there's not a security implication, there's no security bulletin.  We've released again since then, but in this instance, if you're on 26.0.0.126 or higher, you're good from a security perspective.

If you're looking for just a list of what the current available versions are, this is probably a better source:

Adobe - Flash Player

If you're specifically worried about events that require you to take action (e.g. you're a network administrator responsible for keeping your client workstations patched), then you'll definitely want to subscribe to the security notification service and keep and/or keep an eye on the latest Flash Player bulletin.  As long as you're running a specified or higher version than what's listed in the most recent advisory, you should be in good shape.

Hope that makes sense.

The Adobe Security Bulletins page (Security Bulletins and Advisories) shows APSB17-17 as being the most recent.

However, the page it links to (Adobe Security Bulletin) under "Solution" recommends users update to 26.0.0.126, which was withdrawn. The current release is 26.0.0.131.