Using follistim after its punctured

Has anyone used follistim more than 28 days after you first punctured the vial? If so how long after you first punctured it did you continue to use it and was it effective? The manufacturer says 28 days is the limit however I've read a few things online where people said it was still effective for them months later. My friend wanted to give me her 300iu vial but she had to use 20iu's of it 4 months ago so it's punctured. Wondering if I can still use it if I have to go into a 2nd vial to save me from buying a whole new one.