H1B extension beyond 6 years from previous employers I-140

[communicator]

Hello,

    I recently joined a US-based client. They started my PERM process and requested to get a letter from my previous employer. Though I got a letter from the previous employer, the letter contains pretty much same responsibilities as a new employer but with different frameworks of the programming language platform (Java) I work for. 

   Now the lawyer from current employer says we can't use previous employers letter, since it has different tech stack than current emp even though responsibilities pretty much same and suggesting to file my PERM with a subsidiary that my current employer OWNS but operates an independent entity. 

   I got my I-140 approved from my previous employer and if my company processes my GC with Subsidiary,  Can I still have my H1b filed through parent company which currently owns my H1B based on the I-140 which I got approved from my previous employer?

 

Thanks for your response in advance.