Inconsistent End-of-Chain Building Times

[iron0037]

Within buildings.txt, most buildings at the end of a development chain (the level 5 or 6 building) take 2190 days. However, a few inexplicably take 2160 days to build: ca_keep_6, ca_town_5, ct_barracks_5. ca_keep_6 even has a comment saying that the number should be 6 years. I think someone's math forgot a month!

	ca_keep_6 = {
		trigger = { TECH_FORTIFICATIONS_CONSTRUCTION = 5 }
		upgrades_from = ca_keep_5
		build_cost = 500
[COLOR="#FF0000"]		build_time = 2160 #6y[/COLOR]
		levy_size = 0.3
		garrison_size = 0.2
		ai_creation_factor = 97
		
		start = {
			OR = {
				AND = {
					FROM = { religion_group = muslim }
					year = 1360
				}
				AND = {
					FROM = { top_liege = { primary_title = { title = e_byzantium } } }
					year = 1380
				}
				AND = {
					FROM = { religion_group = christian }
					year = 1355
				}
				AND = {
					FROM = { religion_group = pagan_group }
					year = 1500
				}
			}
		}
	}