I just rewatched this after rewatching the other three and again, this was a great closing chapter for this tetralogy.
Upon a second viewing I noticed Billy wearing the green reindeer sweater that Mark was wearing when he met Bridget on NYE 😭
Also they should have included the obgyn played by Emma Thompson in the NYE party to have my S&S reunion (since Hugh Grant and Gemma Jones were there!!)