The High Sierra installer not only installs the new OS but it also changes the disk format form HFS to APFS on SSD drives.  Additionally, it does the required firmware updates for the model of mac that the installer is being run on. Therefore, it may be necessary/easiest to run this installer on each mac before applying a High Sierra image to the mac.  The command to do that is:

/Applications/Install\ macOS\ High\ Sierra.app/Contents/Resources/startosinstall --applicationpath /Applications/Install\ macOS\ High\ Sierra.app --agreetolicense --nointeraction

(obviously you have the “install macOS High Sierra.app” in the /Applications folder for this to work)