360s from three to two piece tops?

[Jimmy-Jim-Jim]

This is another one of my 360 questions! When and why did the 360 change from three piece to a two piece top? While the earlier tops may have been a wood saving device the later tops may have been a labour saving device with one less butt joint.

[libratune]

The change appears to have occurred in mid- to late- 1966.

Don't know why.