Grackles are Icterids or New World blackbirds whereas the blackbirds of the Old World, especially Europe are Turdidae, so very different. This is the problem with common names, some plants can have dozens of common names, eg the wild arum has many names such as Lords and ladies, jack in the pulpit and so on but only one binomial name Arum maculatum. Things like insects, especially mayflies can also have several common names particularly, to fly-fishermen with their duns and nymphs which relate to different parts of the insect's life cycle, some mayflies moult twice as adults before flying, mating and dying, but they each have only one scientific name, the Mayfly, is Ephemera danica also known as a greendrake in it's larval stage. Even here, before scientific protocols were organised internationally, every new 'discoverer' of a species gave it their own one and the protocol now is to agree to call it by the earliest known scientific name where possible. As occasionally, they were well off the mark in their classification some of those have been renamed (and renamed again in light of better information), sometimes when you see things referred to in scientific papers to textbooks one species current binomial name will be followed by several alongside which also show the name and date of the previous name and discoverer or classifier. Science isn't a perfect process but hopefully, it does its best and over time does get it right.