Anyone explain how green slips work on short call?

A person is on SC at the start of a reserve block. They get assigned a next day rotation (unrelated to SC) and rest at the end of short call. Then they get an ARCOS green slip callout for a trip that reports during the SC period but conflicts with the next day rotation. Report time is ~1hr if that makes a difference.

Shouldn’t they just get used off shortcall instead of being offered the GS?
Does being within 24hrs of report for next day rotation matter?

Further, person accepts the green slip. Scheduling then removes the previously assigned next day rotation and awards the new rotation as a short call assignment instead of a GS. ???