Ask which was the fourth Buddhist council and you get two answers, and both of them are correct within the tradition giving them. Theravada Buddhism, following the Sri Lankan chronicles, gives the number to the assembly at Aluvihare that put the canon into writing. The northern schools give it to a quite different gathering, associated with the Kushan king Kanishka and with the compilation of the Sarvastivada Abhidharma commentary.
They are not versions of one another. They are separated by centuries, by a subcontinent, by language and by what was actually decided. The two traditions were not in communication about the numbering and had no reason to be: each was counting the assemblies that mattered to it, in the order they happened, from a starting point they did share.
The consequence is that the Buddhist councils cannot be laid out in one sequence every Buddhist would accept, in the way the Christian ecumenical councils can be numbered one to seven with only the question of who receives them in dispute. Burma later added a fifth and a sixth to the Theravada line, and those numbers are Burmese numbers that the other Theravada countries did not all adopt.
An atlas has to decide how to present that. The honest presentation is to name each council by what it did and where, keep the ordinal as a label a particular tradition uses, and say whose count it is. A single global numbering would be tidier and would be an invention.