Did Herbert Fr\"ohlich predict or postdict the isotope effect in superconductors?

Herbert Fr"ohlich is generally credited with having predicted the fundamental role of electron-phonon interactions in superconductivity in 1950, and in particular the isotope effect, without any experimental input. Here we examine the facts on which this belief is based and point out that whether or not the generally accepted view is true depends on the meaning of the word {\it shortly}.