My general understanding is that Twonky Media was originally developed specifically to be a DLNA-compliant solution. Plex was not, but had DLNA support added as

My general understanding is that Twonky Media was originally developed specifically to be a DLNA-compliant solution. Plex was not, but had DLNA support added as a bolt-on feature to the server. Plex had better UX than Twonky but I don't think any of the Plex clients ever functioned as controllers, so Plex wasn't quite "real" DLNA in the sense that Twonky was, it was more of like a compatibility solution to allow embedded DLNA clients to access your media in Plex (I believe this still works but... don't have any DLNA clients around, so who knows). Twonky was "first-class" DLNA but never felt very high quality and didn't survive to the modern era. While UPnP was accepted as an ISO standard and by extension DLNA was very ISO-standards based, I think the ISO angle tends to be a distraction... the meaningful authority on DLNA, including the specifications and certification, was always the DLNA incorporation itself (a non-profit partnership of its promoters). Many DLNA implementations predated ISO acceptance of UPnP A/V on which its based, and the way to get the specifications was not by paying a hefty sum to ISO but by paying an even heftier sum (membership dues) to DLNA Inc. So DLNA was an "open standard" compared to e.g. Plex that does not intend to be a multi-vendor ecosystem, but it was not as "open" as you would hope which was no doubt a factor in its limited adoption... some device vendors like Logitech and Sony bet on it pretty heavily in hardware products but it probably would have seen more of a software ecosystem if the specs were easier to obtain. This is of course not dissimilar to many other "open standards" like USB (controlled far more by USB-IF than by any other standards body). Of course USB versions are typically submitted to general standards bodies like IEC, but when there's already a domain-specific organization promulgating standards usually the only reason it gets submitted to general standards bodies is for compliance purposes, e.g. it's not unusual for government customers to require that things be standardized through ISO (which is basically the origin story of POSIX). In the case of USB I think IEC acceptance is mostly driven by safety regulations in some countries that require electrical interconnects to be approved by a recognized standards body. I'm far from an expert in this field, this is just what I've observed about the interaction between implementation groups and general standards bodies.