The only source I have seen stating that they crossed in TX in 1984 was a WND story. I have been looking and have not seen it repeated elsewhere, just the 12 year bit.
The way the story was written contradicted itself a bit too as it mentioned no one knew when they smuggled in along with an anonymous border agent quote stating 1984.
Fox News reported this morning that some of the men came across the southern border as infants or small children, grew up in the US.
Sorry, no source on that, but their site probably has more info.