Kinda, sorta.CSX merged these lines:
· Conrail (Consolidated Rail Corporation)
· Richmond, Fredericksburg & Potomac Railroad
· Pittsburgh & Lake Erie Railroad
· Chessie System
· Western Maryland Railway
· Baltimore & Ohio Railroad
· Chesapeake & Ohio Railway
Chessie System was the collection of WM, C&O, and B&O, not a fourth separate railroad, and you completely left out the entire "S" part of CSX - the Seaboard System portion of the original merger (Seaboard Coast Line, Clinchfield RR, and Louisville & Nashville RR, Georgia RR, Atlanta & West Point RR.)
Conrail was not involved in the original CSX merger; Conrail was a completely separate company until the late 1990s when it was divided up roughly evenly between CSX and Norfolk Southern. Pittsburgh & Lake Erie was also another later acquisition in the early 1990s.
You can also add the Port Huron & Detroit RR to the list, which was purchased by C&O/CSX in 1984.