It's same as black mages.
You started to cast fire I and you would see fire III proc from the last fire I. (You used surecast - lethargy - virus or another ability to force server update and check the proc before fire I hits. Was useful during 2.4 and beyond before start casting blizzard III to enter umbral ice).

bards are the same, you use bloodletter, blunt arrow, empyreal arrow, sidewinder and all kind of buffs to force server update and check Straigther Shot proc. Sometimes you get the proc when you are casting, it's a crap and would be fixed. The potency lost is 10 against use heavy shot cast vs straight shot cast. You cast SS and you have the proc, no problem. Let ss be casted, use another oGCD, and use against SS proc.