If they are recent Gaastras then they will be designed for a 12% bend as all the others you mentioned. Its no surprise that they work.
Old Gaastras were designed for 10% bends and NP are designed for 14-15% bends.
There's a world of difference.
This is an old
Gaastra Manic ...
Non-cammed, and unlikely to be older than 2001 from my reckoning, because I don't believe that Gaastra made Manics before then.
Mrgob, do you know what year your Manic is?
Incidentally, even though Gaastra masts are stiffer in the top than the bottom, they still have a very even bend curve (according to Matt Pritchard).
Still maintain that for the majority of sailors who just want to go out and get wet, that NP mast will do the job.