Re: How is it known...ice re****ts

The evidence is mostly from the surviving officers, who remembered some 
messages but not others.  There's also the fact that there are no records
of 
replies being sent to certain messages,  notably the ones from Mesaba and 
Amerika.  Captain Smith replied to the messages he saw as a matter of 
courtesy.

There's room for a bit of doubt, because key officers died.  For instance,

nobody remembered Californian's first warning, which Bride said he gave to

an officer he couldn't name.  Maybe it was Murdoch.

What we can say is that enough warnings are known to have reached the
bridge 
to have cause more care to be taken.
-- 
Dave Gittins
Author of  Titanic: Monument and Warning.
http://users.senet.com.au/~gittins/Book.html