I know this was mentioned before but I could not find the previous posts nor do I think it is relevant form the past 2 months. I have also encountered a bug that gives you in my case 7 ALS ambulances (that I spam bought) for a small ambulance station that has a maximum cap at 6 units. I have been building a lot of small ambulance stations packed full of ALs ambulances today and it's only one station that has this bug. I built 4 all identically and all spam bought and only 1 of the 4 gave me 7/6.
The mysterious ambulance can be called out to missions and can be used as well as a regular one. It is visible everywhere a normal one is as well.
A nice feature to bypass the system and for me to get one extra ambulance but I'm sure it was not intended to be like this.