This script will print the build numbers of the macOS version from all installer apps

InstallerBuilds.sh

#!/bin/bash

export PATH=/usr/bin:/bin:/usr/sbin:/sbin

installerBuildVersion() { # $1 path to the installer app
    installerApp=${1:?"no path for installer"}
    # echo "inspecting: $installerApp"

    if [[ -d "$installerApp" ]]; then
        identifier=$(/usr/libexec/PlistBuddy -c "print CFBundleIdentifier" "$installerApp/Contents/Info.plist")
        if [[ "$identifier" == com.apple.InstallAssistant.* ]]; then
            systemdmg="$installerApp"/Contents/SharedSupport/BaseSystem.dmg
            if [[ -e "$systemdmg" ]]; then
                installdisk=$(hdiutil attach "$installerApp"/Contents/SharedSupport/BaseSystem.dmg -noverify -nobrowse -readonly | tail -n 1 | cut -c 54- )
                installerBuild=$(/usr/libexec/PlistBuddy -c "print :ProductBuildVersion" "$installdisk"/System/Library/CoreServices/SystemVersion.plist) 
                installerVersion=$(/usr/libexec/PlistBuddy -c "print :ProductVersion" "$installdisk"/System/Library/CoreServices/SystemVersion.plist)
                echo "$installerApp : $installerVersion $installerBuild"
                hdiutil detach "$installdisk" >/dev/null
            else
                echo "couldn't find system.dmg in installer $installerApp"
                exit 2
            fi
        else
            echo "no installer app"
            exit 3
        fi
    fi
}

while read -r x; do
    installerBuildVersion "$x"
done < <(mdfind "kMDItemCFBundleIdentifier == 'com.apple.InstallAssistant.*'")