These are all songs that came out from 86-87, Hip Hop's second golden age.
The first golden age was the Run DMC, Whodini, Fat Boys era. The difference is that people started sampling in 1986.
All the groups from 84/85 kinda fell off by 1988 and a new generation of artists came out with a new style. They started sampling.
I'd say the beginning of the "Boom Bap era" was Sucker MCs by Run DMC.