Just measured my 5+ string basses, two are ~16.5mm and one is ~20mm but I couldn't have told you what the spacing on any of them was beforehand. I used to have a 5 string on a 4 string neck conversion, even that was fine for me at the bridge, the nut end was more of an issue.
That said I find swapping between basses with different numbers of strings pretty straightforward, which I know a lot of people struggle with, so may not be representative.