read the official rule from USCIS

my understanding is if you don't file 140 in 180days after your LC is approved, then LC is invalid...

here is the offical rule, read and understand it by yourself...your lawyer also should know it.

http://www.uscis.gov/files/pressrelease/PermRuleLaborCert052407.pdf

Validity Period for a DOL-Approved Labor Certification:

The DOL rule establishes a validity period for those labor certifications that are approved prior to the effective date of the rule, as well as a validity period for labor certifications approved on or after the effective date of the rule. Employers must file an approved labor certification in support of a Form I-140 with USCIS within the applicable validity period established by DOL. USCIS will reject all Form I-140 petitions that require an approved labor certification if the validity period of the labor certification application has expired. USCIS will deny all petitions that are accepted in error when it discovers that the petition was filed with an expired labor certification.