Perhaps I just need new glasses or something.
To my way of thinking, the typeface Century Old Style so strongly resembles the Old Style typeface designed by Alexander Phemister as to be almost an imitation (although, apparently, it does have one change: drastically shortened descenders) - while the version of Bookman with which I am most familiar, the one drawn by Ed Benguiat, also might take some inspiration from it, but still seems to me to be an entirely new typeface, for which Ed Benguiat should get all the blame - and the credit.
Yet, a Google search shows Phemister mentioned most often in connection with Bookman. This may just be because Bookman is vastly more popular than Century Old Style. though, and not because the link is stronger.