This is indeed confusing.....why would they do that i wonder.....i have checked the tables and its GD vs. GD+20 alright....
and what adds to it, i have also checked the holdong tables for all engine variations on other airbus A/C.
P&W and G.E. and Rolls Royce RB211 TRENT on A330
CFM56-5C on A340-300
Rolls Royce TRENT 500 on A340-600
and they all have 210kts and S spd. and
GD!!!!!
My only guess now is that its something related to the V2500 itself, because as far as i know, the CFM tables are like every other engine i looked at....
maybe what you guessed about the N1 range that needs to be avoided for long periods is the real reason behind it, afterall i know that the V2500 fan blades design is sensitive to flutter between 60% and 74% N1 at low speeds (unlike the other engines i mentioned above) thats why they have established a KEEP-OUT-ZONE for it during take-off, so, maybe this is valid in the air as well....