L1B to H1B Transfer (More Worries!!)

Confused !! Worried !!



Hello Expertes



I am get confused over my L1B to H1B transition.



Working with Company 'A' with L1B extension is in process on I797-C reciept as (I94 is already expirted).
Filled H1B with Employer 'B' and it got approved and job placing is still under process (very delayed response from Employer B)



Company 'A' mandate to serve 1 month of notice period as I worked with them since begining for x years want to get my all formality completed to get all employement documents.




Q1 - Employer B is not giving any recipit # not telling my application is w/ COS or wo / COS apart from mail with approval and resume sharing.
How much I can delay (days) to start on H1B if not able to start on 1st Oct?




Q2. If w/ COS - If I would like to take U-turn and continue with current employer no matter what will be end result of L1B extension. How it can be handled and there will not mix up of L1B and H1B application at USCIS




Q3. If Employer "B" fails to give me job earliest, it will be good to continue with them on payroll on paper and looks for other opportunities with them.




Q4. what is the difference between -  w/ COS or wo / COS?




Q5. Is my current employer comes to know about my other application?




Q6. Employer "B" can push to start early and cut short notice period, what will be the consequence in near future for Background checks and during Residentship applications




More search getting more confusion..!! Kindly Advice.