A lot of propaganda is built up around some sort of positive guiding ideology that is rooted in a historical formation, which grew out of that positive ideology but which has transformed out of all recognition of that historical form, thus necessitating the propaganda.
History, being the infinitely complex process that it is, always involves some mythmaking in understanding it, both as it unfolds and then after as it is understood in retrospect, but guiding ideologies do tend to derive their legitimacy by being somewhat congruent with, or descriptive of, or at least consonant with some sort of underlying reality.
And when you're in control and trying to make some sort of state of affairs that is benefitting you last, one of the things to do is to constantly convince those subordinate to you that that beneficial state of affairs is happening because it is good, and that you are all powerful together because of that, and that it needs to continue to exist that way, even as it continues to transform far beyond what it started out as.
The size of that gap between the propaganda and the form that the propaganda seeks to freeze tends to determine what is good propaganda and bad propaganda, even when the organs of propaganda are highly advanced and ostensibly good at what they do. You can't dictate what reality is forever.
