We also send an announcement to libphonenumber-discuss for every release.
Let's say you have a string representing a phone number from Switzerland.
Form validation used to occur at the server, after the client had entered all necessary data and then pressed the Submit button.
If some of the data that had been entered by the client had been in the wrong form or was simply missing, the server would have to send all the data back to the client and request that the form be resubmitted with correct information.
Such changes are not reflected in the version number, and we would publish a sub-minor release if there were no other changes. During most of the year, excepting holidays and extenuating circumstances, we release fortnightly.