Public domain is not the whole story
A film can be out of copyright while the people in it still have publicity rights, and the brands in it are still trademarks. Archive clips are flagged editorial for that reason: fine for documentary, education and commentary, but think twice before putting a stranger from a 1950s newsreel into an ad.
Uploader-asserted licences
Most Internet Archive items carry the licence their uploader chose, which the Archive does not check, and some modern films are uploaded with a public-domain mark they don't deserve. Those items are capped at 'check the terms'. The Prelinger Archives are different: the collection's own curators state that the films are public domain.
Working with old film
Archive transfers are often 480p or SD, 4:3, with title cards at the start. Pillarbox them rather than stretching, or crop to 16:9 if the framing allows. In a sequence, the builder starts long films part-way in to skip the titles.
