They are referred to as Atlantic and Pacific because there are distinct differences between the two configurations.

The Pacific version does not have the Flagship Suite in F/C, but rather offers a more typical lie flat F/C seat. The aircraft configuration is 18F/42C/163Y. The aircraft is also configured for the crew so that 12+ hour missions can be flown according to provisions in the labor agreements.

The Atlantic version offers 16 Flagship Suites in F/C. (For awhile there were 4 Atlantic aircraft that did not have the Flagship Suite since they were delivered prior to its becoming available, however those 4 were recently retrofitted.) There are 35 seats in B/C and 194 in Y/C. These aircraft do not possess the mandated crew provisions that would allow them to fly a 12+ hour mission over the Pacific. The Atlantic version is also used to South America.

Those are the major differences, there are also some differences particularly in coach as to lavatory and galley locations.