I'd like to challenge the assumption that an explicit call for adoption is required if work is mentioned in a charter. Sometimes, if work is mentioned as a possible starting point, that's true. However for working groups like the original XMPP, DKIM, ABFAB and BEEP, where work was mentioned as a basis/as *the* starting point, the question of whether to adopt the work happens as part of the chartering process. I'm not sure that impacts how IPR is handled; in that case I'd expect the IPR to be confirmed/discussed as part of the chartering process.