You could restrict the numerals to be the first not-whitespace on a line and have to end with a point.

But nevertheless you could do a failure, perhaps if the fifth sub point ends with the word "vi." in a single line:

iv. ...emacs ....
v. ......... ends width the word
vi.
vi. ....
vii ....

But with this restrictions it's even harder to fail. Additional you could try to stepp back, if you find double numerals. But even that does not help if the point v. in the example above was the last one.

I think the "right" solution depends much on your data and the demands at (to?) your program.