"I have lost my index finger."
weS might be more natural in this context, yes, though I'm not sure whether that word was known when the sentence was created.
I'm going to assume, then, that this warrior got his index finger cut off in a fight ten years ago but kept the severed finger in a box for sentimental reasons -- and now he's lost or misplaced (chIl) the box and with it, his index finger.
Now that the course is in beta, we can't add new vocabulary to it, so weS can't be introduced in a new Klingon sentence for translation into English. But I've added vIweSpu' as an accepted alternative in the translation from English into Klingon.