I have the same problem! I have 8,747 photos on my iPhone 5s (running 7.1.2) that date back as far as the first iPhone. The other week, I noticed that I can only view years 2013 & 2014 when I click the Photos tab on the bottom left of the Photos app and then scale out to the Years view.
The visible photos in the Years view begin with a collection spanning 12/2/13-1/8/14 and end right before the photos that are currently in my Last Import album.
All of my photos are backed up on my Mac Pro in iPhoto. I can still view the oldest photos on my iPhone by opening the Faces album, selecting an individual and then scrolling up to the earliest photos they are tagged in.
For a while, I also had duplicate albums of all the default albums (Last Import, Last 12 Months, etc.) but that somehow fixed itself last week.
Do you by any chance use the app Transfer Pro? Ive wondered if that could be related.
This is the only post Ive been able to find on the internet addressing this issue.