WafflePool uses PPLNS where N represents many shifts. There is no significance if 0 blocks are found during a shift.
Not sure what you mean about the lack of correlation - my recent blocks found always show up in the pool stats. As far as 'recent shifts', you have to judge over the entire set of displayed shifts - the portion of hashing power you contribute is the portion you will get paid of any discovered blocks.
The FAQ says the following.
How do PPLNS (Pay Per Last N Shares) rewards work?
Everyone contributes shares towards a block solution. When a block is found, we pay out the last N shares that were submitted. The number of shares (N) will be getting tweaked as the pool grows to try to average a shift every 10min.
So it sounds like N is the total number shares in the current shift. I would also take that as the shifts with no blocks have no pay.
The personalized stats recent shifts blocks do correlate with the main stats recently found blocks. I can't correlate the personalized stats earnings log.