We have H371 #297, built in 2005. 

Mast height is 18.5m from waterline to the tip of the VHF antenna (confirmed by measuring tape). I am now in the process of ordering a new mainsail, and after taking measurements my sailmaker has determined the P-value to be 14.52m. This is in line with measurements taken by me last year, but almost 40cm more than wat is stated in the factory leaflet (14.15m). With the (presumed) original North Sails mainsail, I had already noticed that the headboard did not go all the way to the black marker in the top of the mast.

With a 20 year old boat, and being the third owner, you of course never really know what happened over the years, but I can not find any other damage that could be related to a dismasting in the past. Also, mast and appendages are all original Sparcraft and components look aged/worn to the right degree for being 20+ years old.

With 2005 being the last year the 371's were built, could it be that the yard ran out of 371 masts and fitted a taller mast (designed for the 370?) for the last "few" hullnumbers? Has anyone else noticed such a significant deviation from the factory spec in their rig?

This is the current setup on our H371, with what I presume is the original mainsail. You can clearly see that the luff could have been longer :-)

I have tried reaching out to the first owner who used to sail her as "Sea Legs" out of Southampton, without result unfortunately.