Partially updating a page normally don't wear out the flash page, so the normal routine is to just count number of page erases.

But I have seen some manufacturers mention that the storage quality of the other bits are affected by the partial writes. So some manufacturers have given info to not perform more than 10 partial rewrites before erasing the page and rewrite all info. All to maintain the 10+ years of retention.

The wear is the high voltages forcing electrons through the isolation, making the isolation slowly break down.
Must be some wear even when cell not toggles but hard to say how much.