The whole point of variable length records is one can have records of different lengths. And not just two lengths, but an infinite number of lengths. One record might be 10 bytes long, another 100, another 200, and another 1000.
In little computer systems (e.g. DOS, Windows) a record ends with a CRLF (carriage Return Line Feed)
in z/os (MVS) and in Univac mainframe operating systems, a variable length record will NOT end with CRLF, but rather the length of the record is on the front of the record. The file (or dataset) is defined to the operating system as variable length. All variable length records have 4 bytes on the front of the record that contains the length of the record including the 4 bytes.