I will echo what others have said in regards to working on a new musical. Sometimes I have taken the time, after a workshop musical has closed, to work on updating the script and fixing the pagination for the Creatives. Unfortunately I don't have the software on my personal computer to edit the score to correct the numbers on the songs/lyrics, so those items sometimes get left out. On my most recent project, the best I could do was to get the Composer to update any lyric changes in her score. To try to renumber was just about impossible. If the Musical Director and I would agree on a new numbering and he updated the files, there was no guarantee that the Composer would stick to them when she made revisions. It's just the luck of the draw. And when the Creatives decide to entirely scrap Act 2 and make a new one - well, it's all fair game, especially when they decide to start the pagination of Act 2 back at 1.
And yes, Wizard of Oz has been around forever, but as Matthew said, what monetary benefit is there for the publisher to renumber songs? Who knows - perhaps not renumbering the rest of the score after #7 was cut became a sweet reminder to the original team who worked on the piece. Just a thought.
Also - if you were working on a new piece, and had over 20 songs in your show, and you cut #7, would you really want to go through everything and renumber it all? Or would you turn to the company and say, "Hey everyone, #7 is cut. Please make a note of it."