Good idea. It would be not bad to mark neologisms in the texts we produce. Another marking for attested words that are not listed in Helge's Quettaparmas is desirable, too.

I usually make an effort to mark unattested words/neologisms in the accepted way by prefixing them with an asterisk.
But I don't see a reason to give special markings to words that are not present in Helge's wordlist. One can always specify the source of course.

The only reason to mark that kind of words would be practical, since those lists are the most complete glossaries, while not many people are able to search the original sources.