Take a periodic reading of the background over time and make a movie of it and you will see the history of the universe unfolding at the speed of light, as the anisotropy on the map flickers at each angle around the visible sphere of space. Some think the temperature has been and will be declining from billions of degrees down to the now ~2.7K, but I think not, at least not to the extent it would be declining if it was, in its entirety, causally connected to the big bang. The background inflowing wave energy is coming from the greater universe, not our big bang, and contains clues to a history much more distant than our local big bang event. Those are clues about what you say is impossible to know, and yet the clues hidden in the CMB are of interest and at the forefront of scientific observational investigations. Universally, the CMB is probably very consistent when viewed from any location across the potentially infinite arena landscape. Granted, within an expanding arena like ours there might be anomalies related to the immediate arena environment and the particular perturbations of the local big bang event, but on a grand scale the isotropy of the background is the big news; essentially isotropic from any given observation point inside our outside of an active arena, when adjusted for the local wave energy density of the arena. The light we call the CMB has been coming toward us through endless space for billions of years, long before our local big bang occurred within the universal preexisting perpetual shower of thermal radiation. In it is a history of prior events, and it is a history we can see, but don't yet understand.