pete.owens wrote:But newcomers tend not to (there are 33 "unknown" runners in the results from my parkrun this morning for example)
Don't assume that they're newcomers - quite a few will be regulars who forgot their barcodes (I've done it myself!), or even fast runners who were slow that day and don't want their result to appear. (Don't ask me why they do this, I don't understand it either, but it definitely happens at my local parkrun.)