I don't have any recent installations on mine, and it only shows a week of System Restore Points, so I think if you are showing two weeks, that is twice as many as mine.
If you make any significant installations, for example, with Windows Updates, where you install several updates at once, afterwards, you may want to turn off System Restore and back on again. This is because if you have too many recent installations, it may stop working. It will show that there are System Restore Points, but when you click on them and try to use them, after going through all the motions of working, which includes rebooting, it will tell you that the system could not be restored. I would also recommend turning it off and on again each time you play around with its size, as you state that you have done.
I have an HP a1624n with Windows Media Center 2005 (XP Pro)with 250 Gig hard drive. The drive also contains a partitioned Recovery area. Everything was running fine until I reduced my allocated space for restore points from 12% (27,529 MB) to 10% (22,063 MB). At that time, it got to where the only restore points retained were ones from the current and previous day, which was only one or two very recent points. I ran my Norton AV, Ad-aware, Spybot, and CCCleaner. I then turned off System Restore, rebooted, started System Restore and increased allocated space back to 12%.
I still get a maximum of two days of restore points. Before all of this, I had from one to two weeks, or more, of restore points. Did I miss something? Appreciate any help.

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