RER Line E(St. Lazare-Magenta(Gare DU Nord)-then out into the
suburbs); Line 14(St. Lazare[just
extended]-Madelene-Chatlet-...-Bibliotheque Nat) are both newly
constructed lines and it appears that "correspondences"(transfer
points) are different for these than for (most) other lines--you
totally exit the Metro system and then do the transfer.
For example: You can travel from St. Lazare on line E, exit at
Magenta; conduct business at Gare du Nord and with your initial Metro
ticket transfer to any Metro line in that area. In reverse you can
arrive on Line E at St. Lazare, spend some time shopping at the "Grand
Magasins"[Au Printemps, Galarie Lafayette--major department stores in
the area]and then board a Metro all on your original ticket. Lots of
other combinations are possible.
My guess is that the cost would have been prohibitive to have the
transfers all within a single controlled area.
[There are a few older line transfers of this type, but they are in
"out of the way areas."]