No reason, you should interpret this as a total of 3 sets across
The following 2 sets may (or may not, depending on how you feel) contemplate a fatigue drop of 3-5%, so you do your first at 8 and drop a bit for the following 2 so fatigue does not creep up and hits 9
Some other logic that I am missing
My money is on #2, but I would appreciate some clarification.
I wrote it like this because people are different and there needs to be some flexibility with loading. If a person can do 3 sets across @ RPE 8, cool.If they need to take some weight off the bar, that’s cool too.
I had thought that the above instruction was for sets across at the weight that was found to be @8 for that first set (even if this trends up to @9 over repeated sets this was fine/intended). Whereas instructions like “6 reps @ RPE 8 x 3 sets” implied changing the weight if required such that we try keep the back off sets @8 also.
In some templates we have the following instruction for the back off work: “Repeat X reps @ RPE 8 until it becomes @9 (cap at X sets)” unless stated like this is the intention to pretty much always modify the weight such that we keep to the defined RPE for the first set? (the more I type this out the more is seems like overthinking outside the more general guidance of trying to not hit sets @10 intensity all the time)