[JudgemAll]

“Boost” is measured in seconds and is called impulse. Basicaly it is a measure of the amount of thrust and fuel to time consumption. A low thrust high fuel rocket would have similar amount of boost to a high thrust low fuel rocket.

So, it is possible that they put too much fuel in the tanks. Or if they had new engines, they might have miscalculated the actual thrust and needed amount of fuel.

[Yardstick]

It seems like they could have turned off the engines once they had provided the required total impulse.

[Jonah Hex]

Or is it possible there's confusion over "excess boost" and "8 degrees off course" due to translation errors?

For example, posit the Proton trajectory deviated over 8 degrees about the x-axis (see above). For a constant a_rel, this would result in an increased a_z and reduced a_y.

In other words, rather than an orbital insertion, the Proton would eneter a pure ballistic trajectory. To quote Tom Lehrer, "Once der rockets are up, who cares vere vey come down. That's not mein department," says Wernher von Braun.