There must have been some difference between how the word "imprimatur" is used today and how it was used in the past. I was just rereading the section of "The Wealth and Poverty of Nations," by David Landes wherein he discusses the use of the term during the inquisition and times thereabout - and his description agrees with that of KNiZ.
P. 180
'Any thoughts of ending the Inquisition were shelved, and Church and civil authorities joined to control thought, knowledge, and belief. In 1558, the death penalty was introduced for importing foreign books without permission and for inlicensed printing. Universities reduced to centers of indoctrination; unorthodox and dngerous books were placed on an Index Librorum Prohibitorum (1557 in Rom, 1559 in Spain), and safe books appeared with an official Imprimatur ("Let it be printed").'
Also,
"Nor were Spaniards allowed to study abroad, lest they ingest subversive doctrine. That same year (1559), the crown forbade attendance at foreign universities except for such safe centers are Rome, Bologna, and Naples."
