The NAT-Routes are established taking into account wind and weather situation. This happens anew every day. They are designated with A and onward on westbound flights and Z and backward eastbound. The tracks are valid within a certain time interval in reference to time over 30W.
The tracks may be great circles or rhumb lines but most of the the time they are not.
And yes, long-haul-pilots have heard of great circles and rhumb lines...
