Vanilla kernels do not have sub-versions beyond the x.y.z scheme. The patch-2.4.24 tarball is for updating an existing 2.4.23 source tree to 2.4.24, so no need for you to apply the patch.
The latest fixes will always have a new version number, so the kernel including all fixes for 2.4.24 will be 2.4.25. If you really want the latest stuff, you can use the "test" and "rc" patches, but don't use them on production environments.
This applies only to vanilla kernels. Distributors like Red Hat or SuSE often backport fixes from newer kernels to the stock kernel version that came with a distribution, which sometimes can be confusing.