[scolby33]

It looks like it's based on their registration "numbers" written out in the phonetic alphabet in use at the time: https://www.smithsonianmag.com/history/comets-tale-63573615/

[adolph]

Thanks!

Comet 1—registration G-ALYP, dubbed “Yoke Peter,” from the phonetic alphabet then in use in Britain (George-Able- Love-Yoke-Peter)