The non genuine brush bars sometimes have one of two bristles that sometimes need trimming a millimetre or two; depending on application (as they fit three different machines).
Likewise, some soleplates made after-market are also designed to fit several machines so the bars can be in different places sometimes. You may surmise
this is for legal reasons. You may think
that if an after-market manufacturer made them absolutely identical
, Dyson would gleefully sue them, but I couldn't possibly comment