we all know we're not supposed to ignore the differences in the appearance of the Klingons in TOS and later shows.
It was clearly indicated both in DS9 and "Enterprise" that this was visible to the characters in the shows as well.
According to the STO storyline the "cure" to the Augment virus' effects was delivered to the Klingons by the time-traveling B'Vat to the time before Star Trek 1.
So the "ridged" Klingons seen afterwards would not have received "cranial reconstruction" but would have received some kind of genetic treatment to reverse the effects of the Augment Virus.
However I noticed something add:
Klaa in Star Trek 5 was shown with his open vest and his chest looked very much like that of a human.