Realistically (lol) almost any unit is going to be under its on paper strength so you'd probably be looking at 700-800 Ultramarines spread across the entire galaxy even with the non-Codex compliant units.I would absolutely stab a bitch for a Carcharodons box set. They're one of my favorite chapters.
I think the Codex Astartes ideal of 1,000 Marines per chapter has always been kind of an "in theory" thing rather than an "in practice" thing. As you pointed out, some chapters just don't give a fuck about the Codex, while other chapters are chronically understrength because of heavy casualties or issues with their gene-seed (Carcharodons, Lamenters, Raven Guard, Flesh Tearers, etc). Moreover, I think that most of the Codex-compliant chapters are technically overstrength anyway, since they usually have extra specialist Marines on hand to maintain their fleets and motor pools and archives and so forth. Even the Smurfs aren't strictly Codex-compliant, since they have the Tyrannic War Veterans operating as a separate unit, the Genesis Chapter effectively acting as a reserve pool, and now an 11th Company formed by Rowboat himself.
Yeah cool let's keep taking away the only things that make the Imperium of Man different from every other generic scifi dystopian government.I seem to also recall that Guilliman wasn't exactly thrilled with the Marines treating the Codex as holy writ as opposed to a primer on operations. I suspect if he gets the chance to revise the Codex, the frontispiece will look something like the saying from the U.S. Army's Ranger School: 'Here lie the bones of Ranger Jones, a graduate of this institution. He died last night in his first firefight using the school solution.'