When a license exists in a file and insert_license with --use-current-year updates the year, it only does so for the first line containing a year:
* Copyright © 2020-2022 Steve Luamo <steve@luamo.com>
* Copyright © 2015-2022 Leve Stuamo <leve@stuamo.com>
becomes (note the 2022 in the second line):
* Copyright © 2020-2023 Steve Luamo <steve@luamo.com>
* Copyright © 2015-2022 Leve Stuamo <leve@stuamo.com>
This seems to be intentional since the comment in try_update_year_range() says "The change will affect only the first line containing years". But I'm not sure why this limitation exists and whether it could be lifted.