First let me say that the primary literary sources for this time period are positively lousy. Appian -- don't even get me started. And the other often-cited source is Plutarch, who is also no Thucydides or Polybios, to say the least. With that in mind...

The original land legislation brought by Tiberius Gracchus in 133 BCE specifically stipulated that the land awarded to the poor could not be (re)sold. We are very much in the dark about the specifics of this plan. It was to be carried out by a three-man commission (of senators, tresviri agris iudicandis adsignandis), and was to deal both with new allotments and with public land already being occupied, both below and beyond the "legal" limit of such occupation. We don't know what exactly the legal status of the land was to be in either case, we don't know what the criteria of eligibility was for the new allotments (could non-Romans participate?), and we don't know how much land was allotted total or in each case. There is some inscription evidence from 22 years later, the "tabula Bembina," which records a portion of a law ending the (now modified) commission in 111 BCE. It declares all the land distributed by the commission to be, finally, officially private property and subject to the Roman census. This suggests that it was not private property up to this point, but remained technically ager publicus. Further, the law seems to recognize the current owners of the land allotments, suggesting that they were able to be bequeathed to relatives (or others?) in the period between 133 and 111 BCE.

After the death of Tiberius, the literary sources tell us that further legislation allowed the lands to be sold by their new "owners." This doesn't seem to jive with the tabula Bembina, and I'm inclined to side with the inscription over Appian (sorry Mr. Appian; no offense intended). It seems likely that Gaius Gracchus, after his brother's death, legislated that the allotted lands be subject to rent (that is, that they were ager publicus and those occupying had to pay rent to the State to use it). The law of 111 would have then invalidated that, possibly.

Things are even more thorny when we consider Romans vs "allies" (non-Roman Italians). The legislation served, in part, to punish those who had been occupying more than the "legal" limit of Roman ager publicus in Italy. The vast majority of this land was not near Rome, but was scattered throughout Italy. Most of that land had been occupied, it seems, by the non-Roman Italians for decades, if not centuries. These 'landowners,' big and small, were almost certainly the big losers in the Gracchan legislation. If we understand it all correctly, they suffered a net loss of land (and probably a gigantic amount) and, probably, the "poor" Italians got none back in return. The result was the removal of land from the allies en mass. The Latins, at least, had the right of commercium and could theoretically benefit from the allotments, since they could own Roman property. The allies, as foreigners (peregrini), could not, and it is hard to imagine how they would have received allotments. Some point to this as a major factor in the outbreak of the Social War a few decades later, when the Italian allies rose up and tried to replace Rome as the hegemon of Italia.

Roman senators were also big losers in the deal. Many of them, like Scipio Nasica, allegedly held gigantic swaths of public land had done so for generations. The powerful Metelli, also, were not happy, nor was Q. Pompeius. It's no wonder Tiberius was killed. Still, his place on the commission was filled again and it seems to have gone forward with its mandate, despite powerful enemies. Still, we have no idea how successful the commission actually was. There is archaeological evidence of its surveying activity in Italy, especially boundary stones and monuments with the names of the tresviri. There was an increase in the census data, almost 75,000 new registered persons by 125, and that seems to me to suggest that the commission was doing some serious allotting.