all I did to upgrade from 2.3 to 2.4 was copy over new versions of tinycore.gz and bzImage to my /boot directory. Is more required?
With upgrades to some versions, what you did will work.
Sometimes other files also need to be changed.
Here is a simple method which works every time, without being concerned about specific files.
In addition to what you did.
Save a copy of any personal files you have in /home/tc.
Delete /home/tc.
Delete mydata.tgz. This is normally in /mnt/(partition)/tce.
(This assumes you are using both home and backup.)
The computer will then boot the same as a with new installation.