They can coordinate, by not duplicating ea other. So Sen. Murray can pass on his slate to the congressman and than that selection list can be passed back to the other sen. Just because you receive no from one doesn't mean you are not comp. In NY they state if you have a nom from another source we will not be considering you. In NC you can get all noms, but if you have your name in for AFA, USMA, and the MMA you might get 1 for the AFA, 1 for USNA and 1 USMMA. It doesn't necessarily mean you will get 3 to one SA.
It is not uncommon for them to talk with each other. They want to spread the wealth around.
If you even look at the scenario you have given, 1 Sen has announced their slate, now the cong. are meeting and the other sen will be in Jan. That means you could do your cong interview get a nod, than the sen in Jan. will pick from the remaining ones that have not received it yet.
I am only surprised that the Sen is doing it in the end of jan., b/c I thought all slates have to be in by Feb. To me that would mean they are going to rack and stack on paper.