When you say you did an initial install of mce version 8.10 - was this from the DVD (iso image burned to DVD)?
I think you are possibly misunderstanding how it works. LinuxMCE at present only runs on Kubuntu 8.10 or 10.04 and comes "bundled" with that particular distribution. You can't install Kubuntu 12.4 and then MCE on top of that, I'm afraid.
If you're wanting to use Kubuntu 12.4 for other things (other than LinuxMCE) then my personal suggestion is to do it on a separate machine. Others have had quite a bit of success with virtual machines as well (create a VM on your 12.4 machine and install LinuxMCE onto that) which I guess is also an option if your machine is pretty resource-blessed.
But your LinuxMCE server is going to be a 24x7 dedicated machine which potentially controls all your automation, media, telecoms etc. It doesn't need massive processing power but it also doesn't want a bunch of other things messing about with the I/O and network which are the important parts of it.
I hope that helps for a bit of background. If you aren't wanting to go quite that far LinuxMCE may be overkill for your needs and you might be happier with something like agocontrol which may run on 12.4 (?)
Let us know what you're trying to achieve and I'm sure the smart guys can give some pointers.
To answer your question, though, from what you say I would imagine that you have replaced your 12.4 installation with an 8.10 installation so, yes, your updates are gone :-(
