The getOverrideListSize uses FlexibleStringExpander to get the list size but depending on the object type will depend on the value returned and how big the number value is
when listSize is a number and more than 1000, the returned value is 1,000
when listSize is a string and more than 1000, it returns 1000.
Looking at NumberConverters, it always uses NumberFormat. For this scenario, you do need to format the number