It has become customary to represent the sound at the end of words of the "happy" group with the symbol [i]. In the past, the short vowel /ɪ/ might have been preferable. The change is supposed to reflect the neutralization of the distinction between /i:/ and /ɪ/ in this context, since they never contrast. For most speakers of RP and GenAm, the quality of the vowel is closer to /i:/, but it is shorter in duration, hence the choice of [i].
I don't know what symbol did not appear. I used /ɪ/ and /i:/ since they have phonemic status in English, but I'm reluctant to use /i/ in spite of the fact that most dictionaries use it to transcribe the neutralized vowel. That's why I used the square brackets for [i]. Neutralization means that for some speakers it could be /ɪ/, for others /i:/, and for others something in between.