I don't think your numbers are correct. The Border Patrol apprehends over a million illegals every year crossing the border. At least twice that many get away. These numbers don't inlcude those apprehended at the Ports of entry. I don't know exactly how many illegals crossed during the time parameters of your statistic but I'm sure the number of illegal entries exceed 6 million.
They put the current numbers of illegals at 12 million (apprx of course)...and from those issued visas at one time or another over the past 15-20 years that are speculated for vary valid reasons not to have left (once expired) is around 6 million.
The notion that over twice as many get away yearly as we turn back I don't find accurate -