How does pool recoqnize that some shares worth more than others?

I've been thinking the following. Say network difficulty fluctuates wildly. Miners that come only when difficulty is lower will be more productive. How would a pool recoqnize this? Which pool recoqnize this instantly?

For example, this is pretty much what I understand from what miningpoolhub says. It's a PPLNS pool.

Say a coin has difficulty 10000

Block 1 is found after 10k shares
Block 2 is found after 10k shares
Block 3 is found after 10k shares
So N for block 4, based on what miningpoolhub says, is 10k

Then suddenly difficulty drop to 1

Now, each "share" should worth much more right.

However, the way I see it is because Block 1, 2 and 3 requires 10k shares, someone mining block 4 when difficulty is much lower will have their shares worth the same way with someone that's mining block 1, 2, and 3 without caring that productivity is "low" at those blocks.

How does pool in general implement that shares that are given during low difficulty worth far more than shares that are given during high difficulty.

This is important for those making bots to buy hash to send to miningpoolhub because, of course, we would send hash only if difficulty is lower.

One thing I would imagine is to implement N in PPLNS in such a way that N is always proportional to difficulty when a block is found. So if difficulty is really low when a block is found then only few shares get a piece.

Another way to implement this is to have weighted share. So each share is divided by difficulty and people get paid based on those weighted share. Obviously share that are earned when difficulty is lower worths more.

The reason I ask is because pool's difficulty is pretty much constant while network difficulty may fluctuate wildly.