Jay, while most GMAT test takers I've heard from only had one MSR question set, that is not guaranteed. I have in fact heard of a few people that got two different MSR question sets on the actual GMAT.
If you think about it, this makes sense. GMAC needs to keep building new IR questions, meaning GMAC needs data on experimental IR questions. Where will they get that data?
Anecdotally, I think it's unlikely that you'll get more than one MSR question set. But it's certainly possible.
But I think your larger question is about timing strategy on IR. If you haven't yet, I would read the blog post that Stacey Koprince wrote, linked below.
http://www.manhattanprep.com/gmat/blog/ ... reasoning/Good luck!