What's being proposed here seemed so odd, structurally speaking, that I didn't even consider it analogous to a master agreement + follow-on contract structure.

What's being proposed here seemed so odd, structurally speaking, that I didn't even consider it analogous to a master agreement + follow-on contract structure. I'm not sure the analogy is totally a fit - a master agreement should itself be a freestanding, valid contract, no? But in this case the 'base' document is incomplete and invalid. I suppose one could just add the addendum of specific terms at the end of the document and both parties sign off on everything in one go, but I certainly wouldn't want to test it in court.