The contract between SpaceX and NASA required two demo flights (and SpaceX voluntarily did the in flight abort, notice Boeing is not doing that).
They did an unmanned demo flight with Dragon C201, that launched Mar 2, 2019 and docked to the PMA/IDS on the ISS.
Then they did the in flight abort, Jan 19, 2020 with the C205 capsule.
Then they flew the Demo-2 ...
The previous one was also crewed (two crew) but it was called "demo" for some reason - despite taking astronauts to the ISS.
The "some reason" that it was called "Demo" is that it was a demonstration flight, not an operational flight.
How is the recent one different?
It is not a demonstration flight, it is an operational ...
The prior flights where Demo flights, and had test pilots as crew. Crew-1 had "regular" astronauts from NASA and other agencies.
They are all crewed, why is it different? Test pilots vs Passengers.
Think a commercial flight, you won't load up passengers on the first manned tests, you do test pilots and some test crew and such. Then you do the paid ...
Short answer: Three cargo and five crew vehicles.
Gwynne Shotwell answered this
Specifically, Shotwell revealed that SpaceX intends to build three reusable Cargo Dragon 2 capsules, one of which is already completed and in Florida preparing for its December 2nd CRS-21 launch debut. On the crew side of things, SpaceX will build “three more” Crew Dragon ...