Skrubol you are correct, it also appears that the matched pair is to control preload - at least that is what I leared from

https://www.ktaiballbearing.com/prod...tact-bearings/

Matched Pair Angular Contact Bearings, also called duplex bearings, are machined as matched sets. The pairs are furnished with the race faces ground to provide preload when installed. To accomplish this, a gap is provided between the inner races or outer race of the pair.

But the design used where you also fit a nut to the shaft - as long as you use a washer (on outer edge of bearing only I believe) then you can pre-load without a matched pair and saving vast amounts of money :-)