A proposal:

1. Rename category to All Story Missions
2. Change ruleset to "Complete every mission that changes the filename, except CPRACE and STUNT scripts"

Reasoning:

The current definition is flawed and ambiguous. Many things can be interpreted wrongly. What is a mission, what is the completion of a mission, what is a permanent icon. All these things can mean very different thing by just applying slightly different meanings to work (similarly to how Los Desperados is or isn't a dupe depending on the definition of dupe you use)

As such, let's just borrow the definition VC uses, which is equivalent to III, and can easily be attributed to a very specific opcode, 0318: REGISTER_MISSION_PASSED. This gives us a unambiguous and objective definition of what a mission and its completion is, simply the execution of this opcode.

However, there are a few scripts that execute 0318 that we don't want, namely, all races (held in script CPRACE) and BMX/NRG-500 (held in script STUNT). We can't call a category with this ruleset All Missions and arbitrarily not do these missions, hence why the renaming to "All Story Missions" is necessary. This gives us the liberty to exclude these scripts from the definition, and it's the closest to the current category you can get with an objective ruleset that cannot be misinterpreted.

There are a few problems with this definition though.

1. Its name could be challenged. What is a "story mission". Why is this mission relevant to the story and not another. What if in my headcanon, CJ decided to do Vigilante between this mission and the other. (lol)
2. High Stakes, Low Rider would become skippable, as the 0318 execution for this mission is actually inside the CPRACE script. This is currently not a problem, but could be in the future
3. Other relevant story scripts that don't run 0318 become skippable, namely, King in Exile. This is also currently not a problem
4. Driving School becomes unskippable and obligatory
5. Gang Territory, End of the Line 1 and End of the Line 2 becomes skippable
6. I dunno m8 my brain runs at 25fps you guys can probably figure out more

Feel free to post suggestions or arguments for and against this definition.