Shelf life of a lithium polymer battery
For LiPo cells you can not strictly speak of a shelf-life, since they basically start aging the moment the batteries are assembled.

Aging depends greatly on the state of charge and storage temperature. The more they are charged, the faster they age. On the other side they are damaged if they are every discharged below a certain point they are unusable and can not be safely charged anymore (consumer device batteries prevent damage in that case by e.g. monitoring the cell temperature)

One table I could find online (at batteryuniversity.com) is sadly for LiIon cells, but LiPo cells should fare similar. It shows capacity loss vs. storage temperature and state of charge:

Storage Temperature  |      40% charged     |   100% charged
      0°C            |    2% after 1 year   |  6% after 1 year
     25°C            |    4% after 1 year   | 20% after 1 year
     40°C            |   15% after 1 year   | 35% after 1 year
     60°C            |   25% after 1 year   | 40% after 3 months


The thing that makes matters worse is that cells have self-discharge, and normal consumer device batteries have protection circuits embedded in them which consume a small amount of current even if the battery is not being used. So even if you made sure to store all your batteries at e.g. 40% charge, they will not stay at those 40% and slowly drift towards deeply discharged or unusable.

So sadly it's not as easy as to say that such cell have a shelf live of e.g. x years.

Regarding your second question I would refer you to Why are there 3 pins on some batteries?