Like some of the other's who have responded, I have some old favorite sites that I've been hitting for years. Seems every time the soil changes (farming, erosion, freezing/thawing) I find more coins. We are all creatures of habit. But you may need to change your detecting habits. As many have said, go a different direction, change coils, change speeds, use a grid, etc. One of the fields I have had good luck in for years, was the site of an old horse track. Inevitably, I found myself going to the same spots where I've had success throughout the years. That may seem like the natural thing to do. But, when you think about it, after years of digging coins in those same spots, that isn't necessarily the best plan. Now, I make it a "habit" to go toward the areas where I haven't been so "lucky". What I've discovered is that there are coins scattered all over this 40 acre plot. Sure, there may be a higher target concentration where the grandstands were. Or near the entrance gate. But people milled around all over this place, picnicking, resting and playing. Searching "new spots" at the old site has opened my eyes up to just how much activity this place had!
One other note..... the dates on the old coins you found were nice. But those may not be the oldest coins there. The underground RR operated from the earliest 1800's to the 1860's. So if this site was part of the underground RR, the best may be yet to come. Next time. Next time! HH Randy