After not receiving my LC last year, I simply gave up and filed the I-140 without it, never thought I would EVER see the LC. In July, we received a RFE from TSC asking for the LC, AFTER we told them we don't have it, and they will have to ask PBEC for it themselves. The reply was received on Aug 1, since then, there had been one LUD, on Aug 5, and nothing since.
In mid October, more than 60 days after USCIS said I should be getting a response, I contacted my congressman's office for help. I asked them to check with USCIS to see just exactly what's going on with my case. Because when my lawyer submitted a request, he simply got a letter saying call them back in 6 MONTH for case status. The congressman's case worker was extremely helpful, she contacted both USCIS and PBEC (now closed) and found out USCIS NEVER EVEN CONTACTED PBEC, after receiving my reply back in August!!! She somehow managed to get her congressional contact from PBEC to call my lawyer, asking for his mailing address so the original LC can be sent to him. My lawyer received the LC within 2 days, and immediately, he FedEx'ed the LC on Nov 1 to the TSC officer who originally asked for the RFE.
Last week, after hearing nothing for almost a month after TSC received my LC, I contacted my congressman's office again. She (the case worker) immediately filed another inquiry with her congressional contact at USCIS, naming the officer whom we sent the LC to, within a day (Nov 30), she got a email response saying my case has been approved, and on Dec 2, I got the official email.