An official truth is not necessarily untrue. It can even correspond to Universal Truth (in Michaelese). One instance is the time when there was no religious freedom, and so the "truths" of the state church were also official truths, and among these there might be some dogma that paraphrased a universal truth, in which case official truth was also Universal Truth. However, Universal Truths are of so general a nature that official truths are more likely to be, at best, World Truths (such as mathematics), and normally, Personal Truths shared by many people or authorities.

However, an official truth can be something that nobody actually regards as true in private, but thinks that it is generally considered to be true. Truths of this kind change with time, when first one person reveals his or her real opinion, and then another, until the "truth" is revealed as false. I think scientific truths belong to this group, although some naive people may believe them to represent absolute truth. At some point of time they may be the closest approximation to truth that can be achieved, but as is known, science advances, and new truths replace old ones.

Worse kind of untrue official truths are those that are consciously disseminated to serve the interests of some ideology, authority, business, etc. They usually are accepted either for lack of interest and mental laziness: one has no personal opinion or knowledge, and doesn't want to make the effort to acquire them; it may not even occur to one that there might be alternatives, or preference: one simply wants to believe.

I won't go into official truths that are enforced by sanctions. They are no truths, although in some instances they might conform with truth, and so we are back at the beginning...