An AIA magazine is obviously not an M-14 magazine because it does not have the hole for the front magazine detent/catch. It doen't need to be marked because it was originally designed and manufactured for the AIA rifle. This is s significant physical and mechanical difference.
The AIAs originally used adapted M-14 magazines, which were not importable in 10 round configuration. Thus the AIA bolt action rifle magazine was developed.
As written, the law is very specific. A magazine in and of itself may be a prohibited device. The magazine's legal status does not depend on whether or not it is accompanied by a firearm. A firearm's legal status does not depend on the presence of a magazine.