Our cat was three when we adopted her, direct from a family who had had her since she was a kitten, but changed circumstances meant she was stressed and unhappy. We kept her name similar-ish sounding, but different, so it wasn’t too confusing. Think Lizzie to Lily, Maisie to Daisy. We just said her name a lot, and by the time we started to let her out she came to it. Friends of ours adopted a cat called Meadow, and over the course of a month changed it to Dora - they called her Medora, then eventually dropped the Me.
My DP swears cats only know voices, but ours absolutely knows her name, dinner, outside, garden, num (a treat), and NO (kitchen counters). I have trained her to sit, using “nums”, so she know sit too. She is very motivated by greed.
Vesper is a beauty, and lovely name.