No, previous to this leap it's not mentioned outright that the Becketts lost their farm. However, Sam comes from a point in time before the events of "The Leap Home pt. 2" where Tom's life was saved and before "Promised Land" where it's found out what Gus Vernon is doing. The life he remembers is his brother getting killed, his father losing the farm and then dying. Even though he's lived through those history changing leaps (and others), there's never any kind of evidence given that he remembers how they would have altered his life when he was growing up.
By the end of "Promised Land" no information is given that would answer the question of whether or not history changed from what Sam remembered...from the history he lived through. True, Al does say that the bank loans are looked over and foreclosures reversed but he never specifically states that one of those mortgages was on the Beckett farm. It could be that the farm had been lost through legitimate means.
It doesn't have to have been mentioned before this episode for the fact to remain that the Becketts did lose the farm or for the question to exist of whether or not that part of history was ever changed.
Personally, I prefer to believe that the combination of Tom surviving Vietnam and the shady dealings of the banker being brought to light had the cumulative effect that the Becketts didn't lose the farm. Of course, that's my opinion and my interpretation of what could have happened based on the facts that were presented. Someone else's opinion on that matter may greatly differ but that's what happens when you get into the speculative part of a story where not concrete facts are provided. We simply do not know, based on the facts presented, if there was any kind of alteration in what happened to the Beckett farm.
Interestingly, between script rewrites there was a change in what came first, the farm being lost and then John Beckett dying or the other way around. In the version filmed, Sam states that the farm was lost first:
Al, my father worked our farm sixteen hours a day, seven days a week. It was his life and when...and when they took it away from him...well, it was wrong then and it's wrong now.
The script I have appears to be an earlier version. The piece of dialogue I quoted above was instead:
My father worked our farm sixteen hours a day, seven days a week. He'll be in the field when he...when he has his heart attack. A month after we buried him, they were auctioning off our equipment. It was wrong then and it's wrong now.
When you really think about it, even the fate of John Beckett is open to speculation. Going by the excerpt from the script, John was in the field when he had his fatal heart attack. Sam's stating that from his memories...memories that don't include Tom coming home from Vietnam. With Tom around, it's likely that John might not have been in the fields by himself and that Tom could have been with him when the heart attack happened. Maybe he could have gotten his father to medical help in time to save him. Again, though, it's something that's never concretely answered and is left open to interpretation.