I don’t think they make a distinction. ATF has said that adding a brace to an imported pistol does not modify the pistol it just changes its classification into an SBR.
This from their FAQ -
I possess a pistol, which was imported and then subsequently equipped with a stabilizing brace. Does 18 U.S.C. § 922(r) apply to my firearm?
No. Section 922(r), in relevant part, makes it unlawful to
assemble from imported parts a semiautomatic rifle that is otherwise not importable. The implementing regulations of the GCA at
27 CFR 478.39 provides that a person may not assemble a semiautomatic rifle using more than 10 of the imported parts listed in the relevant paragraphs of the regulation. As discussed in section IV.B.8.e of the final rule, the criminal violation under section 922(r) is for the “assembly” of the semiautomatic rifle; therefore, no modification of such firearm would cure the 922(r) violation because the “assembly” has already occurred. Accordingly, a person with an imported pistol that was subsequently equipped with a “
stabilizing brace” will have the same options as anyone else under the final rule. Should that person choose to register the firearm, no further modification of the firearm with domestic parts is required.
Last Reviewed March 23, 2023
No. Section 922(r), in relevant part, makes it unlawful to assemble from imported parts a semiautomatic rifle that is otherwise not importable. The implementing regulations of the GCA at 27 CFR 478.39 provides that a person may not assemble a semiautomatic rifle using more than 10 of the...
www.atf.gov