In general at the time, even though the Church frowned upon people expounding on alternative explanations of the world, you could get away with quite a lot by adding precautionary caveats along the lines of “all of this is just idle speculation and should certainly not be misconstrued in any way as an attempt to contradict the teachings of the Church” to your possibly-contentious books. Osiander as the publisher probably didn’t want to get in hot water. Then again, copyright wasn’t really a thing yet at the time and it is reasonable to assume that not every copy of De revolutionibus in circulation at Catholic universities in the final decades of the 16th century actually had all of Osiander’s preface, especially as the content of the book seemed to gain a certain amount of traction in academic circles.
In any case, De revolutionibus only attracted the attention of the “Congregation of the Index”, the official body within the Catholic Church tasked with censoring suspect publications, during the Galileo affair in the 1610s (and not for want of trying on the part of Copernicus’s detractors since a few years earlier – the Congregation of the Index itself was only established by Pius V in 1571). It should also be mentioned that the “Index”, the list of publications considered inappropriate for Catholic readers which was promulgated by the Congregation of the Index, was not mandatory but a set of recommendations that Catholic countries could adopt as a whole or pick and choose from as far as enforcement was concerned. For example, De revolutionibus was disallowed in Rome but continued to be available in Spain, and remained on the curriculum of the university of Salamanca.
