H1B_User_Bpl

I have my Labor and I140 approved by company A. My priority date is Nov 2012. I moved to company B. Company B started by new labor process and it's in progress. It may take another 6 months to a year to complete. Can I move to company C now before labor started by company B is finished? If company C files a new labor and I140 petition, will my priority date remain the same?

My current H1B Approval notice is valid till March 31st and my I94 is valid till April 10th. My current employer A is planning to file my H1B extension close to March 31st, around March 28th or 29th. Employer B is planning to transfer H1B at around 25th March. Question - If my receipt notice from employer B comes after March 31st (say around April 5th), can I continue working with employer A for 2 more weeks i.e. give a notice of 2 weeks and then join employer B at around 22nd April? As I am leaving employer A, I am assuming they will revoke my H1-B extension once I leave. So my working with employer A till Aprill 22nd would be allowed in that case? What other options do I have. Please suggest.

My H1B approval notice is valid till March 31st. My current employer A will file my H1B extension close to March 31st. My new employer B is working on filing my H1B transfer soon probably by March 6th . I have few queries - 1) If my H1B transfer receipt comes on March 28th, can I join new employer B on April 1st or 2nd on receipt notice or I have to join new employer on or before March 31st? 2) If my H1B transfer receipt doesn't come come till March 31st, my current employer A filed extension on March 28th and on April 3rd my transfer receipt came in from employer B, can I join employer B on April 3rd.? What will happen to the extension filed by employer A?