1) Focusing on the posthumous collections is the best strategy there is right now.
Some people forget publishers are not charities; they are in it for the money, as simple as that. They need a reason --a pretty good reason-- to justify reissuing, say, 10 collections which are doing fine as they are. To persuade them to reissue those 10 collections, you need facts, not what your gut tells you. If you tell them, "Bukowski would never change 'concepts' to own'", they will ask you, "how do you know that?", and then you say, "dunno, I've read everything he wrote, it just does not sound like Bukowski." Well, you know what will happen next, right?
But even if you come up with facts to back up your claims, they're going to say, "why should we reissue something that is selling fine as is?" So you need both facts and a good plan to persuade them it's both necessary and profitable.
Reissuing 10 collections, then, is way more likely to happen than reissuing 23 collections. Not only that, even a kid can see the posthumous changes were not made by Bukowski. But the edits made while he was alive were minor for the most part, and no publisher in their right mind will even consider reissuing 13 collections because you show them a few minor changes here and there. They're going to say, "we do that kind of editing every day!!!"
Not to mention we have no way to prove those minor changes in those 13 collections were not actually made by Bukowski himself in some cases. That alone would put off any editor.
2) Anyway, say you work your magic and you do persuade an editor to reissue the posthumous collections. Great, isn't it? Well, I wouldn't cry victory so fast...
Let me give you an example: A couple of months ago, I tried to re-do What Matters Most... After a few days of hard work, I could track 185 of the 191 poems that make up that collection. I visited The Huntington Library hoping to find 3 of those 5 poems, but they were nowhere to be found. There's some unprocessed Bukowski stuff at the Huntington Library, so they might be there, but I don't think so. The remaining 2 poems were re-titled by Martin and I haven't been able to find their corresponding originals.
I, for one, would not re-issue What Matters Most... --or any other posthumous collection-- unless I could track down all the poems in that collection. It would be a fraud of sorts to reissue something that is not completely genuine. To me, anyway.
Let's say you give it a try and you re-do Come On In! --or any other posthumous collection-- and you can't track down 10-15 poems. Would you even approach an editor to ask them to reissue that collection?
On top of that, it would be a labor of love. Publishers won't pay you much to reissue something that's selling well now. Most probably, you would put a lot of time for peanuts.
I'm not saying it's impossible, but it is definitely a labor of love. That would be fine by me. But not being able to find all the original poems would be too big an issue for me. Maybe some other editor would say, "it's only 10-15 poems, who cares? No one will notice!" Well, I do care. I do fucking care.