DGP There is no command in Tk called [pack-old]. Never has been. There is a command in Tk called [ pack ]. [ pack ] has several supported and documented subcommands that have been the same since Tk 4.0. See
Back in the days of Tk 3, [ pack ] had a different set of subcommands. Those subcommands are no longer part of the official interface of [ pack ], but they do still work. So if you have some ancient script that ran under Tk 3 and used those old subcommands, it's possible that it might still work in a current wish.
No one writing code should use any of those old subcommands of [ pack ] anymore. But someone might notice that [ pack after .w ] actually tries to do something other than return an error, so the old subcommands of [ pack ] are still documented in another man page. That man page can't be called pack.n, so it is called pack-old.n.