Since some questions arose, a clarification about what counts towards "100%".
First of all old school gtas like gta1 or gta2 don´t have any percent counters, unlike the 3d era and later games. It is more an "All Goals" instead of "100%". In some later gta games like SA or V however there are percentage counters, but not every side goal (like completing "beat the cock" missions) counts towards the actual percentage. In old school gtas it is a similiar case, because some goals are listed in the pause screen, while other possible side activities like delivering cars to cranes or getting all bonuses are not. So to avoid any confusion or other arbitrary stuff, only the goals listed in the pause screen should count towards "100%"!
The goals are:
- Missions Passed: Each unique mission needs to be completed. Bugs that have you get double mission completes for the same mission don´t mean that you can do one mission less.. and neither if the counter is broken and doesn´t add up the completed missions anymore. Same thing also accounts for the next goal.
- Secrets Found: Each unique "Kill Frenzy" needs to be found as the menu says, completion is optional. So collecting them is enough, which makes the game register this goal (once, if no bugs happen). Whether you complete it or not doesn´t matter in this game!
- Target Score: You need to at least reach the appointed score, which unlocks a red marker that points to the level exit. Since it is a level based game (where you are supposed to unlock next levels by having target score and then finishing the level), going to the red marker and leaving town is an additional requirement, which marks the level as completed.