Why were there two names for the 1966 Methodist Hymnal?

Why were there two names for the 1966 Methodist Hymnal? (1) The Methodist Hymnal and (2) The Book of Hymns?

The Companion to the [1964] Hymnal says, "The results of the hymnal committee's work were recorded in a 515-page report and sent in January to the delegates of the 1964 General Conference which met in Pittsburgh in April. The first major business session of the General Conference was devoted to the hymnal committee's report. After an hour's presentation and discussion, the conference adopted the report without a negative vote. Two years were spent in editing and producing the new hymnal." (p.61)

Thus, it was the 1960 General Conference that constituted the revision process. Their report was approved by the April 1964 General Conference in Pittsburgh. It took more than two additional years for the hymnal to be ready for delivery (July 1966), during which time the new hymnal was being promoted and advance orders taken. The 1964 date, then, refers to the official acceptance and authorization by General Conference. The 1966 date more accurately reflects the publication date.

It's also important to remember that by this time The Methodist Church and The Evangelical United Brethren Church were well on the way toward merger, completed in 1968. The EUBs had published their last hymnal in 1957, so it was still relatively new. They were concerned about what would happen to their hymnal upon merger and consolidation of EUB printing facilities with those of The Methodist Church in Nashville. Responding to this concern, the post-merger called session of General Conference in St. Louis in 1970 retitled The Methodist Hymnal (1966) as The Book of Hymns and gave assurance that the 1957 EUB hymnal would remain in print for a time.