We present an in-depth analysis of the LISA Pathfinder differential acceleration performance over the entire course of its science operations, spanning approximately 500 days. We find: (1) The evolution of the Brownian noise that dominates the acceleration amplitude spectral density (ASD), for frequencies , is consistent with the decaying pressure due to the outgassing of a single gaseous species. (2) Between and 1 mHz, the acceleration ASD shows a tail in excess of the Brownian noise of almost constant amplitude, with fluctuations over a period of a few days, with no particular time pattern over the course of the mission. (3) At the lowest considered frequency of , the ASD significantly deviates from the behavior, because of temperature fluctuations that appear to modulate a quasistatic pressure gradient, sustained by the asymmetries of the outgassing pattern. We also present the results of a projection of the observed acceleration noise on the potential sources for which we had either a direct correlation measurement or a quantitative estimate from dedicated experiments. These sources account for approximately 40% of the noise power in the tail. Finally, we analyze the possible sources of the remaining unexplained fraction and identify the possible measures that may be taken to keep those under control in LISA.