Teacher 86, PiJing,how to show my working experience in US?

The current company is sponsoring my GC now, (EB2) (master + 3 years working experience, EB2)

Before joining this company, I worked for different 3 US companies for 3 years more totally.

My quesion is , If laid off from previous company, how can I get working experience signed by previous HRs? (this is difficult)

For  I 140 working experience letter,

if not using working experience letter signed by previous HRs, Can I just show USCIS that my paystubs+tax return(w2) and H1bs appoval lettler ?

or something else better way to overcome this?

 

thanks a lot