"So, this old boy was down to his last 1.5 PPM, eh?"
1. I have no idea what the real C-14 baseline is; chart for example only to respond to the "don't work after 1 halflife" argument".
2. I understand the C-14 dating to have decreasing confidence relatively quickly (100 or so thousand years), so I would think C-14 was not the method used.
3. There are other radioactive-decay dating methods with other elements that reach farther back (that cost more $$$ to run) --- no idea what method was used here.
4. I would assume (without knowledge) that (if this scientist is not a reckless idiot, which is possible) 3 or 4 methods are used at the same time to see if they corrollate, as any one does not necessarily give you a lot of confidence. For example --- strata, radioactive dating, similar items with known date ranges found locally, etc. If all combine to give same date range, you have a pretty good idea of date.
Pinging a professional.