You can backup both machines with the following proviso.
Both must have different share names.. If you have setup the new MBP from the old one it is now carrying the same name as the old one (unless you changed it).. You must fix up the names.
I have now turned on my old macbook pro, and it doesn't want to backup to time capsule stating the disk may have been erased.
I don't quite understand why this should happen..
The sparsebundle is not just linked to the name but UUID of the disk. And this could be messed up by the way you recovered instead of migrated the files.
You can attempt to force the old MBP to use the old backup.
See Pondini B5 and B6 here
http://pondini.org/TM/Troubleshooting.html
But if it insists on creating a new backup that is also ok as long as you have enough space on the TC for both MBP and the old backup. If not you should archive the TC and wipe it.. then you can start two new backups .. and keep the old backup on USB drive for a few months until you are sure there is nothing wrong with the install and all the files were properly recovered.
As a btw you should always migrate the files.. not use a system recovery. You might have in fact done that and just using the wrong terminology.. so consider the comment as exhortation to other readers. Do not use a system recovery to a different computer.
