TBH the outbound track sounds fairly fairly "bog standard", close to the great circle route (shortest) and it sounds like you weren't on one of the organised Atlantic Tracks.
As to the North Atlantic tracks in general, they change twice a day both to take into account of the fact there's a bit of a "tidal flow" to air traffic over the ocean - most flights go to the States in the European daytime and the other way overnight. Also the jetstream moves, so the published organised tracks also move to either avoid the headwind or make use of the tail wind.
Result is :
1. There are no permanent fixed coordinates over the ocean, we use latitude and longitudes as waypoints and those lat/longs to be overflown are published along with the track identifiers by the authorities (there is a large selection of fixed, named entry and exit points offshore, but not all of those are used every day).
2. The daytime tracks ( westbound to the States) will usually be set up if possible to avoid the usually westerly jetstream, so on the map they may run an unusual distance north or south of what might appear to be the shortest route.
3. At nightime the tracks are eastbound, from the States, and may well be planned to run in the jetstream.
On your way home it's possible you might have been in an official track (possibly the most northern of the nightime eastbound tracks), but it's also possible you were on what is known as a "random" route to the north of the tracks proper.
There's more detail here:
https://en.wikipedia.org/wiki/North_Atlantic_Tracks