You didn't mention the make model year of vehicle but generally the completely off state is a few tens of mA,
The thing is, the completely off state on many vehicles made in the last 25 years or so, is on a battery saver type circuit that keeps more things energized for a certain time period, during which it is typical to see a few hundred mA.
Depending on the vehicle there are events that reset the higher energy state time-out period, for example unlocking the doors, opening the doors, opening the hood if it has a switch detection, reconnecting the battery after disconnected, etc.
For this reason it is best to have the hood open, leave the battery connected for at least an hour (or research the time out period for your specific vehicle), and when you break a circuit to measure parasitic drain, you should have the multimeter in series with the circuit already so it is never truly broken to result in the higher power state (until time-out). This can be accomplished with alligator clip terminated meter jumper wires, or a second helper for more hands, or other rigged contraptions depending on where you are breaking the circuit.
One test where you do not need to do this, not-break-the-circuit is the connection to the alternator. You can just disconnect the wire at the alternator and see if any current is leaking through it, but your figures of 0.26A-0.27A are typical of just having active circuits until a time out period.
Perhaps more context of the vehicle problem would help. Is the alternator or battery very old? Have you replaced either trying to troubleshoot this? Have you had either tested?