1408. Does the “ghost objects” prohibition of P4 disqualify what is traditionally considered a “double exposure” of the kind made in the 19th and 20th centuries?

Yes it does (assuming the reference is to having semi-transparent scenes overlap in the same photograph).

Newcomers to TTG might assume that manipulations of the film era should automatically qualify as TTG.

That is not the case.

The non-manipulation policies of respected news agencies — on whose policies TTG’s rinairs standard is based — are much more strict in the digital era than they were in the film era, simply because everyone knows that it is so much easier to make undetectable manipulations now than it was back in the film era.

For 19th-century examples of double-exposures and semi-transparent scenes, see #4 in the Key entry on ghost objects.