Squarespace announces orders but not your own edits
The split matters, because it decides which action is instant and which one waits.
A Squarespace order reaches us as soon as it is placed. Squarespace announces those. A stock figure you change by hand inside Squarespace is different: there is no announcement for it, so we look every couple of minutes and pick it up on the next check. Both things are stock movements to you, and only one of them is instant, which is why counting adjustments sometimes seem slower than sales.
In practice this is a small difference and it lands in a helpful place. Selling is the fast path, so the case everyone worries about, the same item going out of both shops within a minute of each other, is the one Squarespace tells us about immediately. The slower path is you running a stocktake inside Squarespace and expecting WooCommerce to show it in the same breath. Give that a couple of minutes.