There is an easy solution to all these problems. You just replace the object of the triplet by another record that also contains date, author, and whatever additional information you want. For example, instead of writing (N3 code):

:proteinA :interactswith :proteinB;

You write:
:proteinA :hasInteraction :interactionAB;

And then you wrap the interaction partner together with the meta-information:

:interactionAB
:interactionPartner :proteinB;
:experiment someplace:massspec01232007x;
:experiment elsewhere:pulldownXYZ;
:Bayes_confidence "0.87";
:lastUpdate "01.04.2008";
.
It's not as beautiful but it works with the existing RDF. This is how I managed protein interaction data from different in-silico predictions some years ago and it worked like a charm.
(As a technical side note, instead of outsourcing things into a separate "interactionAB" entry, the N3 notation also allows "anonymous" blocks of triplets that are directly embedded into the referring statement.)