What is the reason for this discrepancy regarding the CRJ100/200's stickpusher-activation angle?
Your wrote:

a value which, according to the report, would not have been altered by the aircraft's rapidly-increasing AOA

The report did not say that (but I can see how that confusion can arise). It said the 1) flap retraction and 2) increasing g load -- would not alter the AOA trip point of 13.5 -- no mention of rapidly-increasing AOA:

the flaps had retracted a few degrees from 45 and the g was increasing, both of which would cause a slightly higher pusher activation speed; however, there would be no effect on the pusher activation AOA. [emphasis mine]

&quot;Both of which&quot; references the two conditions 1) and 2).

What would alter the trip point however is explained on the page before:

When the AOA is changing, the computer notes the rate of change and, if necessary, applies a correction to activate the protection system ahead of its normal trip points. [emphasis mine]

Which is what the computer did, as explained on page 49 (PDF page 59):

The left-hand and right-hand AOA vane angles as recorded on the FDR were compared with the shaker and pusher boundaries adjusted for the phase advance resulting from the rate of increase of aircraft AOA. This comparison revealed that both AOA vanes reached the shaker trip point, but only the right-hand vane reached the pusher trip point (...) [emphasis mine]

In other words, the trip point would be the AOA phase advanced to account for the AOA rate in the Stall Protection System computer. Which as you noted, was somewhere between 8.7° and 9.4° for the stick-pusher.