I believe they are pretty much the same machine with some exceptions. I do know that the "A" means it was manufactured in Anderson, SC. I did a quick Google search on them, link below.
http://www.oldsewingear.com/faq.html#:~:text=The%20401%20(aka%20401G)%20and,an d%20is%20squarer%20in%20shape
Shari.