The help file shows that it’s the first of the two options. With the inlets it is different, there you need to continue numbering if you desire additional inputs. The same logic holds for pfft~. In max inlets can be of a different type, outlets not.
I don’t doubt that this is true, but for the life of me i don’t see that in the help file.
The help file should probably say: double-click me to view content (referring to the poly~ object). Looking at the content, you can see the logic of inlet and outlet numbering in relation to inlet and outlet creation. (Sometimes help files are a bit cryptic.)