How do I get Time Machine to recognise older backups?

I have a MacBook Pro mid-2011 (I think), operating 10.6.8.

Summary of problem: I dropped my Macbook Pro and broke the internal hard drive and optical drive. As a quick fix I took the old internal drive from my Macbook 13" and am running on that right now (hence 10.6.8 - previously was on 10.8.3). I just bought a new internal drive, have formatted it successfully and am ready to reinstall from Time Machine. I have two backups - one which was made a long time ago on the old MacBook 13" and a much more recent one which I made of the (now damaged) hard drive from my MacBook Pro. However, when I launch the Pro with the new drive, Time Machine only recognises the older backup (which correlates to the hard drive I've been using for the last week or two - the one from the 13"). I s there some way to remind my MacBook Pro of the more recent backup? Can I make it show up somehow? I heard something about pressing option-click on the Time Machine icon, not sure if it applies (when I look at my external hard drive the backup is there, but when I open Time Machine it says the last backup was in 2013 - the older one.) Any help much appreciated, thanks.