Janet created a timeline of the name changes a little while ago. The link is
http://forum.gcmwarning.com/jim-mccotter-gc-history/gcx-churches-escape-bad-reports-through-frequent-name-changes/msg22801/#msg22801. To summarize that post:
The "Blitz" Movement started in 1970.
In 1983, the Blitz became Great Commission International.
In 1989, Great Commission International spit into two entities: the Great Commission Association of Churches (GCA), and Great Commission Ministries (GCM). The latter changed its name to Reliant in 2015.
I'm assuming (though please correct me if I'm wrong) that ECC was part of GCA rather than GCM. If so, then you wouldn't necessarily have heard of the name change at that time.
If I've got anything in this post wrong, I welcome corrections.