I don’t think it goes in numerical order, I’m pretty sure I just used the last 6 wraps of silver grey in slot 4 and then it switched to slot 3 where there is a new spool waiting. At least that’s how I remember it working.
4/11/2023
A week or so later, I used this feature to use up a bunch of left over filament and the AMS seemed to want to run it order from left to right so I’m not so sure and now think it does run in numerical order.