Thanks for the feedback! I agree I need to work on making that part more clear.
The epoch length is configurable by the pool. I haven't gotten far enough to know what a good default is but Ocean, I believe, targets an 8 block window for the share maturity period. So if blocks are found on schedule each share should pay out 8 times. With a large window like this the pool has to get really unlucky for any shares to be worthless, but it is possible.
This site has the best explanation of PPLNS that I have found: https://mintpond.com/b/prop-vs-pplns-vs-pps-mining-pool-reward-systems
The PPLNS visualization is randomized but you can usually see a share that never pays out as well as many shares that pay out multiple times. I should screen record a gif to make it easier to share on nostr.