IMHO, "registered collection" is quite effective and way less bothersome for nurses (although way more expensive, too, due to costs of tests/analysis). No sign-offs, no dealing with Pyxis, nothing - just squirt the excess in a designated (your own set) bottle and dispose it in a closed box at the end of the day. The bottles' content is retrieved and randomly checked chemically so there would be no dilution. Done.
The rest is just another set of nonsense which will potentially lead to royal mess if applied "because it is a policy!" way. A nurse who came to job despite of feeling not so good because of, say, acute synus, can be accused of diversion, checked, removed from workplace and further humiliated because she looks flushed, tired, less energetic, her eyes are red and she sneezes frequently, for one example. Would administration apologize if she comes clean? What if she just takes her prescribed Tramadol for back pain?