Can you spell out the script steps you are currently using so we can see what's going on. Usually such problems are because the script isn't actually telling FMPro to do what one "intended" it to do.
Generally, to Constrain a found set, one enters the value you want Included, and doesn't use the Omit option in the Constrain step.
less than (<) will not find (or omit) empty values. You could try adding a third omit criterion, =, to omit the empty fields.
Adding a third omit to find empy worked.
Didn't know < will not omit empty.
Kind of an odd behavior that empty is not less than 1.
I agree it is curious behaviour, especially as in some contexts (eg. as a portal filter) <1 WILL recognise empty values!