could some tell me what the difference of the following sentence is?

1 It had been sixteen years since he left .
It was sixteen years since he left.
2 It was at least ten years since i had enjoyed a good drink.
It was ar least ten years since i enjoyed a good drink.
3 As they talked,they had reached a house in a dark street.
As they talded, they reached a house in a dark street.

I understand, let’s suppose, that if he left in Christmas sixteen years before, you say now your sentence