Ann: Field Exploration Update - Ivittuut Greenland Project, page-7

Right you are, limits of magnitude and accuracy exist, lab results will have both a statistical sample variation plus correlation coefficient variation. As per your referenced paper, for REE elements such as Yttrium the CC is extraordinarily accurate (albeit below the 45 deg line representing a proportional hand-held undercall vs lab assay).

https://hotcopper.com.au/posts/57617230/single
As per my earlier post, the ASX allows hand held XRF results to be withheld as 'only indicative' when in reality it tells the story to within significant figures. 30,000ppm REE +/- 10% accuracy ... who cares, for an exploration project just starting +/- 10% is market sensitive and should be released as material months before the lab assays are returned. Thus no surprise some stocks rise in price sharply over the period between sampling and return of lab assays....

Well before handheld XRF were invented geo's played the same game of 'cherry pick the best grab samples' best they could with a hand lens and judgement. Nearly all projects start out with great rock chips and much excitement but have much difficulty replicating rock chip success over 1m intervals of drilling for which selective high-grading is not an option. Of course, the core sample results of two days ago were similar point grab samples of 'interesting core' not 1m samples over extended distance. Core grab samples no doubt also informed by hand held XRF friend...

No problems with the process (except imo the ASX should tighten up this glaring market information vacuum), just that longer term investors should understand what grab samples constitute and what testing informed those samples being chosen for lab submission. The implications are obvious... early days and relatively meaningless selective sampling.