In 1979, 5 years before the important publication of 1984 (referring to R. Werner, not G. Orwell), Heinz Otto Cordes formulated and proved a nice theorem on what he called Heisenberg-smooth operators. Upon going through his proof, his ideas clearly show aspects of what would be called Quantum Harmonic Analysis (in the sense of Werner's paper). In the present talk, we will discuss this result from a more modern perspective on QHA. We will show how this result can easily be deduced from well-known facts on embeddings of functions and operator spaces, and we will show how variations of this theorem (e.g., Schatten class versions of the theorem on Heisenberg-smooth operators) can be proven by similar methods. The contents of the talk are based on a joint project with Lauritz van Luijk.