What's the PI Data Archive version you are running? Depending on the version there might be different reasons. Please use a command prompt to figure out the exact build. Here's an example with the commands to execute and an excerpt of the output you'll receive:
C:\Users\gregor>cd /d %piserver%
PI Build Name,390_Release_20120924.1
Please also check if there's an archive registered covering the period *-230days. You can use piartool -al command for this purpose.
Finally chose one affected point and check with the creationdate tag attribute if the point was created before or after *-230days.
Technical Support KB00848 - Backfilling with piconfig has some related background info.