I do not have an answer for the XP.
AFAIR the basic 128-800 (no wing tip fins) did not have a restriction. This would support the logical view that operational limits have been tested.
However i do recall that limits on training stalls for some versions depending on avionic fit, which required the YD to be disconnected - no logical connection with wt or cg.
The BAe146/RJ has a restriction for training stalls which requires a test panel to be fitted with AoA displays for flight speeds less than stick shake.
This considered the risk in the manoeuvre due to increased exposure, opposed to the potential severity of outcome. The 146/RJ never encountered a deep tail-blanking stall in flight test, even though theory suggested otherwise; AFAIR the basic 125 was similar.