Japanese are a nation of honor, they do not lie; however not divulging facts to them is not lying and if not asked directly they will not reveal voluntary. Japanese (as a matter of fact all Asians) in their mentality will aways try and give a better scenario and more pleasing story than actually is. If this mindset is correct for nuclear managers that I doubt very much.
(It is known that co-pilots at Korean Air would say to the captain: "It is fine weather out there today, is it not captain?" actually meaning "Captain, it is dangerous to fly through that massive thunder storm ahead!")
Having said that and noting the resources spent in arranging a close looped cooling system by flooding reactor 1, I can only conclude that the radiation reports of the 11th evening were ignored, not considered or even not known to the planners of unit 1 cooling. Only once their flooding preparation started, only then they noticed things are not as expected which resulted in going through all the available data and brain storming sessions and new insight was found.