I don't think they were used for mechanical CAD,
just
electronic simulation and PCB design.
Calma (GDS,DDM,others) had an Apollo port of DDM
(3D mech) to Apollo but it was drowned out by other
offerings and was not a major seller. They just might
possibly have got out a thousand or two copies, though
but my guess would be more like 100 ~ 400.
If someone found an Apollo with DDM on it I think I'd go
most readily for it. They were fun enough.
John A.