I recently cowrote a paper which came out somewhat long: 40+ pages. We uploaded it to arXiv in this form, but afterwards decided that it would be preferable to publish it as a series of two papers. (It was a natural decision given the length and the fact that it naturally splits into two weakly interacting parts. On the other hand, there is arguably some added value in having a combined version of the paper available somewhere.) At this moment, one of these parts has been submitted to a journal, the other one is still work in progress (the introductory sections need to be written almost from scratch).
What is the best way to record this on a CV/publication list at this point? Of course, it goes without saying that arXiv preprints are not nearly as important as published papers, but it seems it would be honest to own up to all of my writings in some form.
Options I see: a) Just reference the preprint on arXiv, and worry about the rest when the other papers are accepted, b) Mention both the preprint and the submitted paper with an awkward note explaining what is going on (perhaps this should also involve uploading the half-paper to arXiv).
(If relevant, my field is pure mathematics, I'm a PhD student about to graduate. I do need an up-to-date CV.)