Although: Even though I’m not personally interested in this topic, I revisited the original solution (which is still correct) and got to thinking that really all we need to do is get the count of the older Sequential Orders in a way that doesn’t auto update (which is why we need :make static in that solution).
NOW, this should be possible with an SSA like Flow State Scalar (from List Popper & Friends). EDIT: it is possible and what I had written before (formatted as a quote below) was the result of a weird bug wrt plugin test apps.
But, for some reason that action is not synchronous while OTHER simple SSA’s I’ve built recently ARE synchronous with respect to downstream actions.
This is rather mysterious to me, but the net-net is I’m exploring why this is and hope to have a plugin that can help make this technique work in a much more efficient way. (That is, by just returning and locking the count rather than having Bubble actually make a static list. In case you don’t know, a search’s count can be returned much faster than the contents of the List itself.)
I don’t have this quite sorted yet, as it’s my birthday and I am now out having cocktails, but I’ll have some sort of interesting update on this here soon. (Which will either be, “oh hai, here’s a more efficient and scalable solution” or “oh, hai, here’s why we can’t have nice things”.)
And here’s my update 
that explains how to do this and why it may be better than using :make static in may cases.