What was the figure of the output of boots for? What was the actual figure? Why does it not matter what Winston changes the number to?

"For example, the Ministry of Plenty's forecast had estimated the output of boots for the quarter at one-hundred-and-forty-five million pairs. The actual output was given as sixty-two millions. Winston, however, in rewriting the forecast, marked the figure down to fifty-seven millions, so as to allow for the usual claim that the quota had been overfulfilled."

Any statistic really didn't matter. THere could have been no boots made. These figures were spit out by the Ministry of Plenty to keep the socio-political illusion alive.