Keeping this thread up but to add:
- for literature, Porsche photographed cars in spring even it was for the following new MY i.e august.
Which means literature commonly used older MY in their prints.
Some photos got retouched, others pics simply left as they are even they have been older MY models, as on this postcards.
For brand-new models they showed pre-production cars from the factory production in spring announcing the new model line-up produced starting in august.
In one instance (1970 2.2l catalogue) they even showed a model never to be sold/marketed (911S base).
Some lterature got printed twice to adjust prices for the new year (most pricelists) and/or changing photos with the now the real production MY model. (some catalogues).