The only thing I can think is maybe some people are behind caches, or their browser is caching an old version of the availability data. I make sure i'm not getting cached data, and was loading it every few seconds this morning so we could see how quickly things sold out.
Unless someone wants to show us a reservation of a black or a jet black iPhone Plus, i'm going to stand by saying there was zero stock of either today, anywhere in the UK (from 6am to now)
Apple helpfully provide the data as one big blob which I process after i've captured it, so it's not like i'm checking each store and each model. I get the exact same snapshot of data that powers the reservation site.
The site went live between 06:01:03 and 06:01:16.
It's stupidly long, but here's the raw data.