Difference between Standard push forward and Mixed push forward

Hi all,

I am currently working on modeling OCA by Prony's series. And I am searching for the helping documentation of ABAQUS to see how Prony's series for viscoelasticity works. I find that in the version before v6.9, abaqus uses a Mixed push forward scheme for finite strain viscoelasticity:

http://130.149.89.49:2080/v6.8/books/usb/default.htm?startat=pt05ch18s07abm12.html#usb-mat-ctimevisco   

Yet for v6.9 and later versions it uses a Standard push forward scheme:

http://130.149.89.49:2080/v6.10ef/books/usb/default.htm?startat=pt05ch19s07abm12.html#usb-mat-ctimevisco

Can someone tell me the difference between them and will these two lead to different results?

Thank you.

Tiankai