Football substitution is an issue I am currently researching. Although the sources speak a clear language. But there have been many exceptions in football substitution, as match reports show.
I know of exceptions in some countries on the European mainland between the First and Second World Wars. The four British associations also knew about this and tried to press FIFA to comply with the rules first. But in the end (1931) they unofficially let the continental European way continue. It had already become a common law there in the few years it had been in existence, and it was much appreciated.
In this post I give an overview of the development of football substitution as far as I can draw/describe it at the moment.