Motorola created Onsemi in 1999 as a spin off semiconductor manufacturer so I imagine that some older obsolete devices may not have any data sheets available prior to the change to Motorola's company model. If someone has a Motorola catalogue dating before 1999, that number may have a reference to what it is.
As a side note, the Ceramic Flat Pack is still available to this day. So seeing a microchip with long wire leads won't necessarily indicate vintage. For example, Texas Instruments W, NDA HKK packages are still active. These would be used in extremely high vibration and/or extremely high inertia environments. Not generally used in automotive or consumer products but more for aerospace and military applications.