What is excat rules related to Labour portability and I-140 portability.My H1B,6 year limit is due Nov-2012.With my Current employer(A) I have Labour approved in 2009 and I-140 filed in Oct-2009 but not approved yet.If I switch to a new employer(B) to whom I can transfer my H1B visa and subsequently proceed my GC can my priority date attached to my earlier employer's(A) labour application be ported to the new employer's(B) GC proceedings?or do I have to wait for my I-140 to get approved with earlier employer(A) for the the original Labour application dates to be portable to new employer(B).Also is it true that I have to wait 6 months after my I-140 gets approved with current employer(A) to move to a new employer(B) so the original priority dates can be ported.What to take care B4 I switch?