I-140 approved- multiple employer changes - Is priority date retains?

[bsspandu]

Hi,

I need help regarding Green card - employer change.

My I-140 got approved with employer A. Then Company A got MERGED with company B in 2016 december.
I asked company B to start my GC processing and they told, only GC amendment is needed. No need to file GC again. But company B never filed my amendment of GC.
Summary: My I-140 got approved but never transferred GC to the new merged employer B.
Q1:: Now incase if i change my employer to C then can i use the same old priority date from employer A?  
or does Priority date will be carry forwarded only if i have approved amendment filed from employer B? In that case i cannot change to new employer till few years.

Q2:: now I have approved I-140 from employer A. 
What if I transfer to employer C before, my current employer B file GC amendment. Then I transfer to employer D, before employer C file GC.
Summary? What happens if non of my future employer files GC for me till 2020. Can my future 2020 employer G able to use the priority date of employer A?

Please advice.

[directory0818]

pd belongs to you whether any future company applies or does not amend your old employer gc