Who can use the New ATF eForm 4?

The ATF released the eForm's site with the ATF eForm 4 that can be used by individuals to transfer NFA firearms to other individual's, gun trusts, and other legal entities.  But who can use the ATF eForm 4?  

When you are using the ATF eForm 4, you will need to add the firearm to your application on the firearm screen.  In order to add a firearm that you are transferring on that screen, you will need to know the ATF control number from the already approved tax stamp.  All ATF eForm approved firearms, whether it is an ATF eForm 1 or ATF eForm 4, will have an ATF control number that you can manually enter if you know or you can use the transferor's social security number to find the ATF control number.  What happens if the transferor's approved tax stamp doesn't have an ATF control number?  Unfortunately, if the transferor's approved tax stamp doesn't have an ATF control number, then you won't be able to use the new ATF eForm 4.  In that case, that transfer from the transferor to the transferee, would need to utilize the paper ATF Form 4 and isn't able to be used with the ATF eForm site.