I have those same brochures, and the S&W numbers are clearly bogus. They used one ammo marketing brochure until 1978, when the industry testing procedures changed away from unvented test barrels (11 inches in the .357 mag). In 1979 they started using a new ammo brochure which said "Note that the velocity and energy figures are based on actual guns, not test barrels."

In the one year difference between the brochures (the same year that test barrels were no longer allowed), the velocities dropped over 20% in most loads. For example, in 1978 and before they said the .38 Special 110 grain JHP +P ran at 1380 FPS. The next year the same load was listed at 1050 fps from a 4" Model 10.

When the testing procedures changed, 'truth in advertising' became a requirement. Manufacturers could no longer market their ammo using those unrealistic numbers that users had no chance of achieving in their sidearms.