In theory, only those who were here before January 1, 2007 are eligible (as well as certain of their relatives).
In reality, millions more can and will sneak in and claim such visas because the documentation required to prove one was here before 1/1/07 is a complete joke. It can be nothing more than an affidavit from a non-relative attesting to the individual's presence here before the cut-off date. Unbelievable.
There is an application period for farm workers. They have to apply within eight years.
I think the reason for inconsistency among sections is that the bill is really a bunch of separate bills hastily strung together.
Now let's take it one step further and assume you're caught. What's to prevent anyone from either denouncing their citizenship and/or claiming that they're not really a citizen since under some 14th amendment claim that their parents weren't under US jurisdiction.
These might appear to be far-fetched scenarios, but I can practically guarantee that if the financial incentives become high enough in favor of illegals vs citizens, we'll see more & more of these stories.