aside from retouching as you mention, photographers often did "combination printing"
where they would mate 2 ( or more? ) negatives together to make a print.
they often did this with scenes that had a sky. an example of his was in the movie
"photographing fairies" ... the photographer would ask a family to bring an old photo with them
to his studio, and he would mate it with their dead son's photograph ( died in the war ) to give them one last
photograph of their "living son" ...
it doesn't seem too far of a stretch to imagine photographers exposing for clothes in one exposure and then the portrait for the second exposures
and mating them in the darkroom. if they were still doing wet plate work they could easily peel the celluloid image, place it ontop
of the other, and make a contact print with the 2 negatives. this could be done with 2 prints too, the same way
we we would cut and paste elements from one photograph to another, rephotograph it, with pencil work to mask combination
(this was the technique used in the movie i mentioned ).