I doubt that applies to VyOS.
VyOS uses a squashfs filesystem as base for each version along with an overlayfs to make any changes persistent for that particular version/installation.
So when you upgrade VyOS except for the configfile itself nothing is remained from the old installation (well content of /config is copied to the new overlayfs).
You can just reboot back to the old installation due to the above design of VyOS.
So what happens when you perform an upgrade is that the new squashfs is copied to a directory in the storage and an overlayfs directory is created. Then the content from /config is copied to this new overlayfs directory.
Finally the box is rebooted.
Upon boot the migrationscripts are runned comparing the “magicstring” at bottom of the config file to know if they should be runned and in that case which scripts should be running. They are versioned per config section.
So if you got one box with 1.3.2 and another with 1.3.7 I would go for the latest stable (or nightly depending on if you want 1.4 LTS or 1.5 current) and go straight from whatever version you currently have installed.
The same migration script which is being runned when you do 1.3.2 → 1.3.3 → … → 1.3.7 → 1.38 will be runned when you go 1.3.2 → 1.3.8.
Actually newer VyOS might have fixed issues in older migrationscripts so going 1.3.2 → final version is safer than going 1.3.2 → all versions in between → final version (that you end up at today).
And if ■■■■ hit the fan just reboot the box and you are back to your 1.3.2 (select that in the boot menu) as it were before you started the upgrade.