This only applies to the 1900D.
The 1900A/B/C manual says minimum flight crew: One Pilot.
1900D Airliner
Section II – Limitations
P/N 129-590000-3ETC1
Page 2-11
MINIMUM FLIGHT CREW
The minimum crew is one pilot. See the Kinds of Operations Equipment List in this section for required equipment
Page 2-30
KINDS OF OPERATIONS EQUIPMENT LIST
SINGLE PILOT OPERATION ONLY
1. Headset
2. Boom Mounted Microphone
3. Emergency, Abnormal, and Normal Procedures Checklist
4. Kit 114-5042
Remarks and/or Exceptions: All passenger seats in excess of nine (9) must be rendered nonoccupiable by “DO NOT OCCUPY” seat belt tube assembly.