some people have said pos coins can be generated even if the wallet is not left running?
no, you have to keep it running to generate PoS blocks with the associated "interest".
However, you don't need to keep it running all the time. Coins accumulate coin-age even if the wallet is not running, and they need a certain minimum age before they can be used in creating a PoS block.
does the wallet need to be left running or even if it was closed for a few years will you open it to find interest added coins?
No, that's not how it works (see above). Coins accumulate age (no running wallet required). The accumulated coin-age can be used in PoS-mining a block (running wallet required), which will generate "interest". The age is capped though, so you should run your wallet every two months or so.
also if the wallet is locked? what happens? the coins are generated but can't be added to the wallet until unlocked or the coins are not even generated?
PoS mining does not happen while the wallet is locked.