You are very correct. The 1965 and 1966 steering columns will interchange. The 1967 and 1968 steering columns were the first generation, energy absorbing (EA), collapsible steering columns. The steering column jacket was known as a mesh jacket. For the most part, these "mesh" columns only interchange within the 1967-68 model years.
This jacket (with all the diamond cutouts) was not very rigid. So this type steering column required a very large, three and four capsule, mounting bracket to provide some rigidity to the whole steering column. Otherwise, the steering wheel would bounce up and down when driving down a rough road. GM also knew that Federal anti theft legislation was going to require a locking steering column in 1969. So with the added weight of the ignition lock cylinder and steering wheel locking mechanism being added to the steering column head, the already whimpy steering column was going to get even worse.
So Saginaw Steering Gear Division invented a steering column jacket with a new method of absorbing energy. They created a two piece jacket with a series of ball bearings that were indented into the area between the two different diameter jackets. This was the 2nd generation EA steering column.
This invention was known as the "Ball EA" jacket. As the two jackets telescoped on each other the ball bearings would plow grooves into the jackets and absorb energy. This jacket was considerably more rigid than the old first gen jackets and only required a light weight two capsule mounting bracket. All GM passenger cars started using this type, 2nd generation, EA, steering column beginning in 1969.