Before moving ahead, please carefully consider the long history of how NTLite has supported SetupComplete, and its OEM workaround. All changes must respect backwards compatibility, because we have too much historical weight.
Here's my proposed fix:
1. Continue providing OEM SetupComplete as a non-default option.
2. When selected, NTLite writes a Setup\FirstBoot\PostOobe runtime script, which looks for OA3xOriginalProductKey.
3. SetupComplete is only executed if an OEM key is present, otherwise the script exits.
This logic prevents SetupComplete from dual execution on other PC's without keys. Nothing needs to be renamed, users don't have to learn anything new. A few factors come into play, as both Wscript/Cscript and WMIC are deprecated, and will eventually become optional features. Maybe PS can be a lasting solution?