What I said was misleading. When I moved the Pages 09 application by itself to my wife's Mac running Yosemite, (where it had not been previously installed), and launched it, I got a warning about it not being compatible. However when I ran the iWork 09 installer on my wife's Mac , then it was good to go.
However, when I upgraded my MBP to Yosemite, I had to do nothing extra because Pages 09 had been installed prior to the upgrade, and whatever it needs to run, was still in there somewhere. 🙂