Do we require previous employers experience certificates for GC process.??

Question

I am in a process to transfer my H1b visa to a different employer. 
My new employer would be filing GC process soon after the transfer. 
Since I will leave my current employer without serving 3 year contract they wont give me experience letter for the past 1 year which i worked with them. 

My question is during Complete GC process, will experience letter from past 1 year is required or does GC process requires Experience letters from all employments. 

Are there any alternatives or options to show experience with my previous employer for GC process?

Answer 1

Yes, you need to have all previous employers

Answer 2

Yes, You will have to submit experience letter of all your previous employers.