Has an NPB (Japan) game ever ended 16-4?
Yes. NPB (Japan) has seen a final score of 16-4 23 times. It first happened on May 2, 1954, when Hankyu Braves beat Daiei Stars, and most recently on August 27, 2022, when Tokyo Yakult Swallows beat Yokohama DeNA Baystars.
That makes 16-4 the 112th most common final score out of 223 that have ever occurred in NPB (Japan). One point away, 17-4 has happened 15 times and 16-5 has happened 18 times.