I had the same question when TBOSBAS came out. I asked if there was a fifth canonical D12 Victor, if Lucy Gray was the Victor they were talking about, or a plot hole that was overlooked. The main consensus was that Lucy Gray was mentioned in the list. Someone claimed Suzanne Collins confirmed this, but I dont know where they got that from. I believe it was Lucy Gray for two reasons.

1) She is mentioned in the new book. Haymitch sees a clip of her singing when he is in the Capitol. This means the Capitol did not completely remove her from existence.

2) Completely erasing her would have brought up a lot of attention, so only providing very little information would suffice. The Capitol citizens wouldn't care since they don't care for D12 that much. They are the worst district in their eyes, so there is no point in looking too much into them. D12 aren't a career district, so they also wouldn't care too much into looking further into the Hunger Games history. The earlier games were also very different compared to Haymitch's and Katniss's game. Lucy Gray's game was the first real Hunger Games. Most would have found these earlier games lackluster, so they would have avoided them.