Boatman's right on the helmet, and that's also probably why MD's often declare that their contribution is not recorded on the official report.
It comes down to two things.
One, the excavation report is just that. It's the report of what was researched, revealed, excavated, recorded and interpreted by those who worked the site.
That 'ought' to have at least a mention in the prior research of items that were reported as found on the site. However, that comes down to proof. A Roman helmet found above a Viking layer ? yeah, I'd doubt that. Not saying it couldn't be, after all the Vikings did trawl the world for treasure, good things, etc., but, I would really need to see secure context to believe it.
Secondly, it's back to secure context. Is there good, clear, recorded evidence that that particular helmet came out of that site in that particular context ?
It's not that we personally might not believe the finder, but we cannot prove it, and we cannot prove it with enough clear evidence that it can be given provenance.
I believe that's what Boatman's post was trying to say.
As for spiking the ground with ringpulls….how about those who salt the ground with cheap Roman coins and tesserae to get Archaeologist involved in an attempt to stop building works ?
Swings and roundabouts.
M