Yes, you are correct. I immediately remembered the previous example of "between" when I saw your solution.
And I thought it would work like the other one does, despite the wording.
However, when I tried, it showed me all Titles leading off with 1-9 but
not 0. When I added the "OR" statement, it returned 0 as well.
You probably already know how to test if you haven't yet (or don't already have Titles leading off with the full range)
but to stay with the theme of clarity/specifics, I would just
create test folder > copy a file into it > rename it > paste again > copy those 2 > paste again >
copy those 4 > and so on until you get 10 files > rename beg. of filename with the full range of leading number >
scan into library > rename title > Apply filter statement(s) to MN.
Here is my "at beg." mask (without "OR")
<Group|Name:MN Technical (editing 1)>\<Group|Name:Finalize-correction-trap>\Title (#s at beg)|Position:Before|Child of:Now Playing|Filter:SubStr(<Title>, 1, 1)|Show if
Mine may just be off on some detail or something weird going on in my environment.
Anyway, it's not a big deal for me. I can just use the additional "OR" statement.