It seems that Microsoft is using the very old SIE standard with only 3 digits. There has since several years back been replaced by a new 4 digit serie. It is very much used in almost every Swedish company and facilitates the export and import between ERS systems but also when working in TAX systems.
I suggest Microsoft to take a look here for more information. It certainly will facilitat a lot to have the 4 digit funciton in D365. I use it very common in other systems where it is a standard.