Archived data are only available for spots on the main list (not for custom spots). For most spots the archive starts when the spot was added to the list.
"Statistics" are not based on real measured values at the location! It only comes from data produced by the forecast model. Every model cycle (every 6 hours) the archive is filled with the nearest forecast values. Every night the statistics are regenerated based on the archive data.
Wind - number of days show the number of days for each month when at least X Bft wind was forecasted for at least 3 hours of the daytime (daytime = approx. 10 a.m - 5 p.m.) Day temperature - average forecasted temperature during daytime (10 a.m - 5 p.m.), Night temperature - average forecasted temperature during the night (approx. 22 p.m - 4 a.m.)
Score is a number which rates the quality of the spot in a given month based on how windy it was. For each 3 Bft day the spot gets 1 point, for 4 Bft: 3 points, 5 Bft: 5, 6 Bft: 7, 7 Bft: 9, for 8 Bft: 10 points. The final month score is normalized to 30 days so that different months are comparable.