need more sulphite

OK, true confession time.

I made my first wine (from a kit) about 8 months ago. For the last ~6 months it's been bulk aging in a soda keg. At the time I added some extra metabisulphite like the instructions said to do if you were going to age the wine for more than 6 months.

I also homebrew beer. A week or so after I racked the wine to the keg, I kegged a batch of beer. I force-carbonate my beer after kegging ... and, well, one soda keg looks pretty much like another ...

So there I was with sparkling merlot. I figured it would eventually degbutt itself if I kept depressurizing it, but it really never did. I took to violent keg-shaking every time I walked by for a week, but it was still fizzy. I wanted to bottle it before Christmas, so I finally got a serious paint-stirrer at the hardware store (one of those ones that looks like a squirell-cage fan) and fired up the drill. That seemed to do the job, so I then bottled it (about 2 weeks ago). It tasted fine then.

Now I've been reading more and I discover that I probably should have added more metabisulphite when I bottled it. Worse, it seems that what sulphite was there may have been dispursed by the agitation (although I'm still a little fuzzy on that part).

So my question is - how long will this wine last? Should I open up all the bottles, add some metabisulphite, and re-seal? I put a bunch of it in .5l beer bottles with crown caps, so it's not all that big of a deal to do this. I expect most of the wine to be consumed in 2 to 6 months, but I would like to keep a few bottles for a year or more. Should I just doctor the ones I'm going to keep?

Thanks for the advice ras