Andrew,
The meaning of "source or origin" in trademark law is considerably different than the meaning used in your email below.
In the trademark context, the "source or origin" referred to is the source of the goods or services currently being offered to a customer, not the source of the idea for that service. It is a "present day" analysis: if I am buying these goods or services today, the trademark identifies a single source that is providing me the service or manufactured the product that I am now buying. Originally, this was construed so narrowly that trademark licensing was prohibited. Over time, by obligating a trademark owner to actively engage in quality control over the goods and services (and to reflect that in a contract), trademark licensing was allowed. The trademark licensee is not viewed as the "source or origin" of the product or service -- the trademark owner (i.e., the licensor) continues to be the "source or origin," even though they are not physically manufacturing the product or providing the service. The "goodwill" (or reputation) that comes from making a good product or offering a good service accrues to the benefit of the trademark owner, not the licensee.
"Source or origin" has nothing to do with "genesis" or historical foundation; for trademark "source" purposes, it doesn't matte where the idea for something comes from or where the function was first created, or even where "standards" (in the sense of parameters set by a standards-setting organization) are set. All kinds of goods and services must conform to external standards, whether set by governments or by non-governmental standards-setting bodies (e.g., the ISO). And of course, those standards-setting bodies do amend standards from time to time.
So, when looking at the question of "source," the questions to be asked in the IANA context by someone receiving a service from the IANA group at ICANN are the following: "Do I believe that the responsibility for the execution of the service I am receiving today lies with ICANN or with some other source? Do I believe that how well (or how poorly) that service is being provided (e.g., how timely, how accurate, how professionally) is the responsibility of ICANN or of some other entity?"
I believe that the answer in both cases is "ICANN." That does not denigrate the role of the IETF in any way.
Nor does it mean that ICANN cannot move from being the "source" of the services to being a licensee, by transferring the IANA marks to a third party and entering into a trademark license. However, that would mean that this third party would need to exercise active and ongoing "quality control" over the services being delivered by ICANN (and potentially, some other IANA service provider); that is not something that the IETF (or the IETF Trust) does today.
Another important point: It's not necessary to argue that the IETF was always somehow the "source and origin" for IANA services in order to propose the IETF Trust as a potential home for the IANA brand. That would also be a "present day" analysis.
However, the argument that the IETF has always been and continues to be the "source" of IANA services for trademark purposes does have several unintended consequences. First, the IETF has never entered into a license for ICANN (or its predecessor as the IANA service provider) to use IANA or Internet Assigned Numbers Authority as a trademark. The IETF has never exercised "quality control" in the trademark sense over ICANN or its predecessor (or if it did, it stopped a very long time ago). The IETF has never challenged the trademark registrations owned by ICANN or its predecessor. All of these things would lead to a finding that the IETF had abandoned the trademark and that whatever claim it once had to the trademark is extinguished. Conversely, if the IETF was the rightful owner of the IANA trademarks at the time that the current registrations (or the earlier registrations assigned to ICANN by its predecessor) were applied for, then ICANN and its predecessor committed "fraud on the trademark office," since the applicants claimed (as required by law) that they were the rightful owners of the marks and that they know of no other party that could make a claim to own the marks in connection with the relevant services. The end result of "fraud on the trademark office" is that the current registrations would be void and subject to cancellation by the trademark office. Ironically, ICANN could then reapply to register the marks now without "fraud on the trademark office" so long as it established that the IETF had abandoned the mark. (Alternatively, if ICANN established that the IETF was never the rightful owner of the marks, the current registrations would not be void.) There's no reason to subject the IANA trademarks to these risks -- and frankly, there's no basis to do so either.
Hope that helps.
Greg