You can make this work by having the 1st century start on the last day of 1 BC. Think of it as an overlap if you like; it doesn't really matter. That allows fo

You can make this work by having the 1st century start on the last day of 1 BC. Think of it as an overlap if you like; it doesn't really matter. That allows for consistent zero-indexed centuries. It doesn't have any other practical consequences that matter.