It rests on what the people concerned believe to be real. At the very least, there has to be an absence of violent opposition, including the threat of secession.
合法性不仅仅是符合法定程序那么简单，它还取决于相关人员认可什么是真实有效的。至少，不允许存在激烈的反对，包括“脱离联邦”之类的威胁。