According to historians both Adams and Leverrier used Bode's law to guess the distance to Neptune, which led to a vast overestimation of its orbital period (Adams - 227 years, Le Verrier - 218 years, actual - 165 years). Apparently, their estimate of Neptune's mass was also largely off. Nonetheless, both came up with a position in the sky close to each other's, and to the actual one:"The only actual value they were close to, if one looks at the table, is the location in the sky it would be found. It is possible that both men were simply lucky with this. We shall never truly know."
This is somewhat mystifying. The first thought is that their errors in distance and mass "compensated" each other, although I am not familiar with this type of calculation to tell if this makes sense. But it should be possible to tell if they were "simply lucky" or not. For instance, is the prediction of Neptune's position in the sky based on the parameters they assumed correct only for a short time period or more broadly? Is it the case that visible orbital deviations of Uranus only determine some function of Neptune's distance and mass, but not each value separately? And was their value close to the actual one? Did anybody look into these kinds of questions? Is there a "reason" for the correct prediction despite the erroneous estimates, or were they indeed "simply lucky"?