If the cable is the 'lead in' from the supplier's line, there is no ringer wire, just the line 'A' and 'B' wires. They will probably use the blue and orange wires. The ringer wire is derived from the master socket.
This type of 4 wire cable became obsolescent when the present style of phone sockets was introduced, so it was probably re-used from a previous installation.
Before modern sockets came into use party line connections were common, and line polarity was used to identify the called line, so the line could have been connected either way around.
The master socket should in theory have been the first socket connected, but in practise it could have been placed anywhere as all the sockets are connected in parallel.
So you've really got to open up the existing sockets, and see what is connected where in each case, otherwise you may be able to connect a socket that will work with one phone, but will stop everything working if the phone is swapped.
Some handsets use the ringer connection, and others don't, so swapping two different types around when the line connections on a socket are reversed can have unpredictable results.
The old wiring convention for 4 wire telephone cable was:-
Blue - Wire 1
Orange - Wire 2
Green - Wire 3
Brown - Wire 4
The cable construction was one twisted quad. Because of it's single quad construction, it shouldn't have been used to carry two seperate lines.
Modern cables all use twisted pairs.
