What exactly do you mean by "numerical order"?
Generally the Twine 2.x application stores a project's passages in the order that they were added to the project, although there are a number of things that can influence that order after the fact: Passage Deletion, Importing a project, etc...
Each passage that is added to a project is assigned an integer PID, which is unique (& sequential) within a project. There are a number of things that can cause these PIDs to change after they have initially been assigned: Passage Deletion, Importing a project, etc...