There was still controversy about software copyrightability in 1974. That said, I expect IBM still explicitly copyrighted their implementation of SQL (and licensed it [1]) as they had first started doing with some of the System/360 software during the prior decade. Note that, in 1974, you still had to explicitly copyright something; it didn't just happen automatically like today.

[1] As a side note, IBM may not have been the first to license software but they certainly helped make it a standard practice. When they unbundled much of the System/360 software, they felt that copyright was a weak protection (given its uncertain legal status) so they combined it with a license.

> it didn't just happen automatically like today.

... in the US of A.

Berne convention started a little bit over a full century before that.

Impressive that the superfluous “need” for the Copyright (c) YYYY notice still persists to this day in the mind of many.

There can still be advantages to being explicit as I understand it to enforce copyright/collect damages. For example, most people don't actually deposit copies in circumstances where they're technically supposed to.