As already said , the manufacturers are covering their back sides.
I don't see how a rack can have a max load of say 10kg when their boxes weigh half that weight.
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With loading up boxes and panniers common sense should be taken, spread the load evenly, I used to load my vee with wey over the recommended values with zero issues, except when it fell over then then I had a problem ..
Geez ... I miss that bike ..