What we now call “open source software” existed before 1998, but the phrase “open source software” wasn’t in widespread use prior to 1998, and any pre-1998 uses of the phrase don’t have the current quite specific meaning.
The FSF promoted the phrase “free software”. The “open source” term was chosen as an alternative because (1) English “free” is ambiguous (price vs liberty) (2) the FSF’s strict ethical stances weren’t very corporate-friendly and so “open source” avoided the association with FSF which was seen as alienating many corporate executives (3) it represented a broader range of acceptable licensing conditions than the FSF’s strict ethics would allow
There's no need to pick such nits. The point was clear: "open source" -even with very loose definitions of "open source"- was one key to Unix's triumph over Multics. BSD was "open source" even in 1978 because Bill Joy did nothing to verify that recipients of BSD source had AT&T Unix source licenses. Eventually BSD became truly open source when the AT&T-Berkeley lawsuit was settled -- truly open source by the standard you mention, even though that was before 1998. That no one spoke of "open source" in 1978 is neither here nor there. Multics is practically unused by comparison to Unix. The End.
UNIX was proprietary licensed code developed and owned by AT&T / Bell Labs. You had to pay for a license. The source was distributed to academic institutions and OEMs/VARs–but not always the customers of those OEMs/VARs. As such, in some ways it was less "open source" than Multics was–every Multics customer got the source, but not all end-users of UNIX (buying it through an OEM/VAR) did.
The first freely available (without paying for an AT&T license) distribution of BSD was Net/1 in 1989. (And even that was under a legal cloud which was not resolved until the USL vs. BSDi lawsuit was settled in 1994.) Active development and marketing of Multics was terminated in 1987, although bug fixes continued to be made for existing customers until the last customer site shut down in 2000. So the statement that "UNIX is open source but Multics is not" wasn't true in the relevant timeframe, and differences in source model aren't a good explanation of the failure of Multics vs. UNIX's success.
> BSD was "open source" even in 1978 because Bill Joy did nothing to verify that recipients of BSD source had AT&T Unix source licenses.
I haven't heard before the claim that Bill Joy distributed BSD to non-licensees–which, if true, probably violated the license agreement his employer signed with AT&T. (Prior to Net/1, BSD lacked a clean separation between code originally developed by Berkeley, and modified AT&T code). If a person distributes source code in violation of license agreements, does that make the source code "open source"?
