What are consquences of h1b approved petition before oct 1st?

Currently I am working on a L2 EAD, my employer had sponsored H1B with COS which is approved for FY2014. 


Company B is willing to hire and want to apply for H1B transfer before Oct 1st. 


If H1b transfer is approved before Oct 1st , can I join company B before Oct 1st?

Is it safe to apply for a H1 B transfer before Oct 1st when I am not currently holding the status?

In case of denial of the transfer, Can I work for old employer without any issue as if the transfer never happened?

In case the transfer is approved and employer A revokes original petition, does the new approval hold good?

Will the approval of petition with new employer make me ineligible to work for current employer?

If the transfer is approved, do I have to compulsorily start working from the petition start date or can I join at a later date and work for Employer A on h1 till then?

Once approved, you can join B on EAD itself before Oct 1 and then continue working them after Oct 1 on H-1.

H-1 transfer can be applied even when you are not in H-1 status as long as you are maintaining that other status (l-2 in your case)

New petition holds good even if A withdraws their petition.

If COS is approved for Oct 1, then you have to work on H-1 from Oct 1.