They apply to those copies you added the notices in and any copy made from those with the notice. If nobody ever has made a copy of a version without the notic

They apply to those copies you added the notices in and any copy made from those with the notice. If nobody ever has made a copy of a version without the notice, that effectively means that all published versions now are under that license and that nobody may use it under another license, because they have no legal source of it under any other license. If there's already copies been made, those copies remain under the previous licenses if any (which may be "all rights reserved" as the legal default).