GM model numbering 4101-4108 why no 4105

[siberyd]

I was asked and don't know the answer.

Siberyd

[roadrunnertex]

Per the Modern Intercity Coaches book by Larry Plachno on page 37 he states.
Production of the PD4104 model ended in 1960.
A fancy demonstrator coach had been floating around which was assumed to become the model PD4105.
It never did get into production and the PD4105 model number was never used.
RRT