I think Ryan and I are not particularly shaming you about testing. I for one think you are being too hard on yourself. This is primarily a mistake by the designer and (now that we know more) the client. WTF are they thinking in not allowing you to test the transaction? They should slap themselves with the blame (but of course they won't).
As for comments vs. classes -- classes can be class="seenote123" that can refer to separate documentation. Packing stuff into comments is messy, and the (sibling?) comment nodes will never be completely tied to the element, as opposed to classes right on the element. You could use data- attributes instead of classes. -- S.
