While gathering data for my Roller Coaster Rankings spreadsheet, I discovered that I had to add two separate entries for each twin coaster. This is because some of them have differing stats, and in order to calculate things accurately, they needed to be listed separately. Objectively, a twin coaster has two different track systems, which means it is worth two credits, but only if you ride both of them. If you only ride on one of the tracks, you only get one credit.
As for Mobius coasters, I treat them like twin coasters by having two separate entries, with the total track length of the ride divided in half for each entry. So, for my purposes, a mobius coaster has two credits in it, but again, you have to ride both parts to get all the credits.
On a related note, Steeplechase at Blackpool Pleasure Beach has three separate tracks, so it has three separate entries.