How to mount an APFS formatted volume created on macOS 10.12.1 on macOS 10.12.2? According to this thread from Apple Developer Forums, an APFS volume created on macOS 10.12.1 is not mountable on macOS 10.12.2, because of the incompatible changes.

I put some important files in my external drive formatted as APFS, and now I would like to access the data. I tried this:

diskutil apfs list


This:

sudo fsck_apfs disk1s2


And this:

diskutil apfs addVolume disk1s2 APFS MyVolume


The error message is similar to what mentioned in the above thread:

$ diskutil apfs -IHaveBeenWarnedThatAPFSIsPreReleaseAndThatIMayLoseData list

======================================================================================================
ENUMERATION OF ALL CURRENT APFS OBJECTS
   apfs call: sizeForContainer: err=-69808="Some information was unavailable during an internal lookup"
   apfs call: freeSpaceForContainer: err=-69808="Some information was unavailable during an internal lookup"
|
|-- APFS CONTAINER REFERENCE = disk1s2
---------------------------------------------------------------------

$ sudo fsck_apfs disk1s2

** Checking volume.
** Checking the container superblock.
error: nx_incompatible_features has unsupported flags: (0x1)
   Container superblock is invalid.
** The volume disk1s2 could not be verified completely.


My questions are:


Is there an official utility that help me to mount the volume?


Or to upgrade the old APFS to the new APFS?

Is there any way to downgrade my macOS 10.12.2 to 10.12.1?


I don't have "Install macOS Sierra.app" in hand, is there any "secret" way to download a previous version of macOS? (I mean previous versions of Sierra, not El Capitan or earlier releases)
I don't have Time Machine backups or similar. I would like to fresh install macOS 10.12.1 on my old MacBook, mount the volume, and copy it elsewhere.



Thanks!
I guess you'll have to try find someone still on 10.12.1, or who has the installer. 

Lessons learned:  


Don't use betas for mission-critical tasks.  
Keep installers.  
Keep backups.