PPLNS difficulty changes

In the FAQ, it says " [...] regardless of round boundaries we always consider the last (difficulty * 2) shares." 

If round 1 is long, round 2 has low difficulty but is short, and round 3 has higher difficulty but is also short, might shares issued early in Round 1 get included in Round 3 that were not included in round 2?    Consider share #11: Round 1, with difficulty 15, is hit with share 32, so share 11 gets a piece of that, then round 2 has difficulty 10, hit with share 36, share 11 is too old... but then Round 3 has difficulty 15 again, and is hit with share 39, so shares from 10 through 39 get a piece?

When difficulty changes during the round (many coins change difficulty every block, so there can be hundreds of difficulty changes during a round here), are all shares of the round treated equally, or is a share contributed at difficulty=10 considered twice as valuable as a share contributed at difficulty=20 ?