I have seen Kietts here in June also, but suspect that this is because some plantations stimulate flowering with KNO3, so that they produce at that time.
at the moment seems we are at peak Kiett season here, they are being sold all over the place.
but this year seems off anyway in regards to mango ripening times. I bet I will still see Keitts this year way into Oct. and maybe even into Nov.