I'm one for umbrella explanations -- when possible -- to rationalize seeming contradictions.
For example, in the 1986 RETURN TO SOUTHFORK prequel movie, they should have filmed at the Box Ranch, not yet burned. Later in oldDALLAS, mention that the ranch house was hit by a twister only a few months after Bobby brought Pamela home ("must've been an omen," remarks JR). And since the prequel was filmed at the "new" Southfork anyway, state that it was burned in the '60s, reconstructed as the Box Ranch, and then was hit by that twister in 1978 and again reconstructed out of nostalgia to look like the original house we saw in the prequel and most of the series.
Stupid? Yeah, but what are you gonna do?
And that doesn't fix the fact that the prequel has tiny Bobby & Pam meeting at a barbecue in 1951 when neither of them were born yet, given that it was specified in 1980 that they were both born in late 1952. Never mind Bobby's headstone showing his birthyear as 1949 (but that was a dream, and we know Pam always misremembers ages) and that his I.D. card when he was kidnapped early in the first full season shows he was born in 1966 and therefore just 12 years old.
So then you just explain that someone mis-recalled those dates.
Barring that, that aquifer under Southfork that Jeremy Wendell poisoned in 1984, which caused the Ewings to perceive Mama with a different head for a year, was still having its long-term effect on the family's memory and cognition. Thus, any discrepancy can be corrected.