Surnames for girls are still popular in the US whereas in the UK they've declined since the 1980s. A good chunk of those bottom half names are surnames, which are still semi popular for boys only in the UK.

I wish the axis were of equal length so it was square. Are the bubble sizes the combined number by country? Interesting graph!

I've made a list the outliers in this post (not op). It covers more than one year, back 1996, and it's a list if the names with the biggest difference.

It dips back down to baseline 9 months after August 1 1914 for fathers but stays elevated even past the end of the war for uncles.

You have an even more interesting graph where it shows the rate of transmission falling back to base levels after May 1915 and for the rest of the war. That's about 9 months after deployment. Also interesting that fathers who were at a greater risk of dying were more likely to have their name passed down. Uncle name transmission lasted at elevated levels into the 1920s. Also interesting that daughters were also named after their fathers.

Edit: realized it was OC and reworded.