Getting off in the weeds a bit on titles, but here's the text from the Texas DMV title handbook regarding motor and frame numbers in regards to VIN. I would assume other states are similar.
1955 and Prior Vehicles
On 1955 and prior model motor vehicles registered and titled in Texas, the motor number
is the principal means of identification, except Ford products manufactured since March
31, 1932. Motor numbers are die stamped on the engine blocks. Raised or die cast
numbers are part numbers and should be disregarded.
Beginning with the 1956 model motor vehicles, the number on the body or frame is the
principal means of identification and known as the "vehicle identification number (VIN)."
The words "permanent identification number" and "serial number" are sometimes used to
refer to the official VIN.
1955 and Prior Vehicles
On 1955 and prior model motor vehicles registered and titled in Texas, the motor number
is the principal means of identification, except Ford products manufactured since March
31, 1932. Motor numbers are die stamped on the engine blocks. Raised or die cast
numbers are part numbers and should be disregarded.
Beginning with the 1956 model motor vehicles, the number on the body or frame is the
principal means of identification and known as the "vehicle identification number (VIN)."
The words "permanent identification number" and "serial number" are sometimes used to
refer to the official VIN.