For software preservation reasons, I've been trying to sort out the licensing for a lot of 40-year-old CP/M code with an intent to liberate as much as possible.
Back then formal licensing was very rare, and what we now call open source was handled on a very informal basis by 'public domain' libraries. (Very little was actually public domain.) People would donate things they wrote to the libraries for redistribution. Except, there was hardly ever any kind of actual license.
Here's an example of the kind of thing I'm dealing with:
;***********************************************************************
; MICROCOSM ASSOCIATES 8080/8085 CPU DIAGNOSTIC VERSION 1.0 (C) 1980
;***********************************************************************
;
;DONATED TO THE "SIG/M" CP/M USER'S GROUP BY:
;KELLY SMITH, MICROCOSM ASSOCIATES
;3055 WACO AVENUE
;SIMI VALLEY, CALIFORNIA, 93065
;(805) 527-9321 (MODEM, CP/M-NET (TM))
;(805) 527-0518 (VERBAL)
(From http://www.retroarchive.org/cpm/cdrom/SIMTEL/SIGM/VOLS000/VOL005/CPUDIAG.ASM.)
So: it's got a an actual copyright declaration; there's a statement that it's been donated to a user's group; there's no actual license; the original author is unlocatable and potentially dead; the user's group itself has no formal licensing or even documentation other than a few text files describing which archival tool to use, and no longer exists outside archives (see http://www.retroarchive.org/cpm/cdrom/SIMTEL/SIGM/VOLS000/VOL000/).
(This is actually unusually clear, as there's a statement in the source that it was actually donated. Frequently there isn't.)
I've been very cautious and have been going by the principle that if I can't locate the actual author and persuade them to put a real open source license on it, I can't use it.
Is this actually true? Is there any basis behind the frequently-expressed opinion that as it's been freely distributed for 40 years then it's legally safe to continue to do so?
I'm pretty sure there isn't: while you could plausibly argue that the author's intent is clear, in that they wanted the software distributed, there's nothing indicating the terms of distribution. (Non-commercial use only statements were pretty common back then.)
But I'm an engineer, and tend to think in terms of rules. Second opinion, please? I'd love to be wrong here.