I think you are looking at the chart incorrectly, as the chart is a graph of daily or weekly imports. The data I referenced are totals for each month. Thus, in a short period of time the imports may be zero, but for the month they would remain high.
It is still possible to generally estimate the daily average even though the chart space per year is very compact.
The highest line is 300,000 barrels a day, so nothing even comes close to 500,000 per day.
The chart average is 93,000 barrels a day.
See upper left corner.