The title expected me to see the common 48k model, not the rarer 128k one.
The paper itself says "a stock 128Kb Spectrum" which is confusing for those who weren't aware of this model.
In the Iberian Peninsula, 128K models were all over the place.
Not really in UK or other European countries (besides the Amstrad almost-knockoff).
It is strange that on UK, Speccy birthplace they were apparently rare, given all the Crash and Your Sinclair magazines I owned at the time, and related content.
Amstrad bought Sinclair in spring 1986 and they ran down the remaining 128K+ stock, meanwhile the grey +2 was already ready to manufacture - they'd already designed the case and reversed engineered the 128K+ to get a head start. It was in the shops by that autumn.