The mis-application of that Jesus saying seems to have begun very early! if they were baptizing infants in the first century. Even t Paul may have baptized everyone in a converted family. Though it might have been more the 'Christian initiation' primarily.

Of course 'Limbo' used to be 'taught' -- which is what 'doctrine' means. Doctrines start off as 'theological opinions'. That's what full and official and infallible doctrines – like the Assumption of Mary – were for all those centuries before being 'proclaimed' officially. 

It was a 'theological assumption' but not yet an ''infallibly taught and official 'doctrine'. And even now, some argue Mary died first, like Jesus did, and 'tradition' claims -- while some argue she got 'assumed' without having to die.