I talked to one barista and she said do that but I did two decalf one half calf and one full calf

Darryl van horn?

Hmm I would have given like 2/3 decaf of a shot and then 1/3 full caff. Still
One shot

If you have the newer Mastrenas you can pull 1/2 decaf shots for 1, 2, or 3 shots and it'll do the measuring for you, on the old Mastrenas you can only pull 1/2 decaf two shots at a time so if they wanted 1/2 decaf for a single shot drink you would pull a shot of each and pour out half or pull two with the 1/2 decaf setting and pour out half of that
Can't comment as to what the exact standard is but that's generally how I've seen it done when the person ordering it isn't right in front of you to clarify with

There is a button that on the machine that does it automatically. You can only do 2 or 4. But yeah if you need less, then you pull as much as you need and toss the rest.