How to replicate:

Start Taxi Driver during the mission "Cipriani's Chaffeur", after the Laudrette cutscene (It's a triad ambush!). Starting it before the cutscene is a regular Taxi Driver dupe, starting it during the cutscene is a crash.
If done correctly, the game will present the usual pager message for Taxi Driver completion "BIGGER! FASTER! HARDER! new Borgnine taxis open for business in Harwood. Call 555-BORGNINE today!", along with the percentage increase

Nice find! Have you checked to see if this works with any other vehicle sub-missions, (Vigilante, Paramedic, etc.)?

Not yet. I checked Taxi Driver first because it was the easiest to do so. Vigilante has 6 seperate completions (three for 10 criminals in each island, three for 20 in each island), and Paramedic has 3 (35 and 70 patients saved, beat level 12), while Taxi Driver only has 1 (100 taxi fares)

So this means 100% will have not a single fare? Wouldn't the checklist have to be adjusted to that, since it shows the amount of fares, obviously

Who needs the checklist anyways