I apologize for the bump...
Most every manufacturer has a difference engineered into their lock, the cylinders use different
keys and the mortise lock cases generally have different spacings for their hardware to fit. These
manufacturers couldn't secure patent rights for their products if they were too closely copied.
For example, a Baldwin mortise lockset could use a Sargent or Medeco cylinder with the proper
cam, but you couldn't take a door having a Bouvet mortise lock and hardware & substitute a Baldwin
mortise lock without also changing the hardware to Baldwin as well
billdeserthills
Mortise cylinders and interchangeable cores are two different things. Mortise cylinders have a standard diameter and thread pitch (1 1/8" diameter - 32 TPI), but come in different lengths for different door thicknesses and, as others have pointed out, they take different cams depending on the lock being operated. The door must be opened, a plate removed, and a set screw backed out to remove one of these for re-keying.
Interchangeable cores use a special control key to remove the core without having to open the door or backing out any set screw. BEST is the most popular for small format IC's, and a number of manufacturers (Schlage, Yale, etc.)
https://secretstorages.com/best-mortise-locks/ have their own designs for large format IC's. The benefit of interchangeable cores is that a building can be rekeyed quickly, so long as they have the control keys and documentation.