I’ve been going through the Metadata Working Group specs here:
The consortium of companies in the group are responsible for a good deal of the consumer and professional devices that might be used for creating, manipulating, or storing digital images, so it has a good deal of bearing on what we’re discussing.
You can download their specifications document, which is good to look at and consider how their standards compare and contrast, as well as augment or potentially clash with the Getty documents or other standards we’ve read.