The law operated in most of the Proto-Indo-European daughter languages, with notable exceptions being the Indo-Iranian and Tocharian branches in which the difference between long and short PIE diphthongs was clearly preserved.
Compare: The term Osthoff's law is usually properly applied to the described phenomenon in Ancient Greek, which itself was an independent innovation from similar developments occurring in Latin and other Indo-European languages.
Osthoff's law is, in some version, valid for Greek, Latin, and Celtic but not for Indo-Iranian and Tocharian.
Some examples might be: The traditional school of Balto-Slavic linguistics posits compensatory lengthening of liquid diphthongs before laryngeals.
Moreover, they reject Osthoff's law for Proto-Balto-Slavic, and reconstruct long vowels intact, but only if they are inherited from Proto-Indo-European.