According to the UIC's conventional rules, any official first name ending in a vowel, except for "E," which could be either, indicated a female. On the other hand, a name ending in a consonant usually signaled a male. Exceptions were very rare and mostly indicated an Immortal parent.
Nicknames on the other hand were often given and did not follow the same conventions. They were typically chosen by official name shortening or by the individual's preference, and misadventure or random happenstance might also play a role. It was not uncommon for nicknames to change several times throughout a person's life.