Resolve the initial financing statement a UCC-3 will amend, from
the file number and file date the filer copies off the UCC-1.

The search a filer must run before creating a UCC-3. Resolution is
three-way: a UCC-1 the organization filed through Baselayer resolves
to that submission; a filing known from the public record is claimed
as an imported filing (creating the record if this is the first
claim, exactly as POST /lien_submissions/import would); and a
filing Baselayer cannot verify at all is reported as not_found —
unless allow_unverified is set, in which case it is held as an
unverified imported filing built from the details supplied here.
Keep allow_unverified off until the filer has seen the not_found
answer and confirmed they want to proceed anyway.

The resolved filing is what POST /lien_submissions/{filing_id}/amend
then targets. warnings flags a file date that disagrees with the
matched filing, a date past its lapse date, or a filing that is no
longer Active — none of them block the lookup.

The file number is validated against the state's format where the
format is known (length and character checks otherwise), and the
file date must not be in the future nor predate the revised UCC
Article 9 effective date (2001-07-01).

Not available to sandbox applications: the lookup reads the real
public record and can claim a filing off it, so there is nothing
to simulate.