This seems similar to the problem I experienced back in April where I had gone 1538 miles on 44 gallons of Diesel and an unknown amount of used vegetable oil. I had to split my fill up into 2 separate entries so that I could have an accurate miles driven. 1700 miles will work for me, though 2000 would be even better. I'm currently at ~1400 miles on ~14 gallons of diesel, and I don't bother keeping track of my vege oil use, since I figured out it cost's me $0.04 (yes that is 4 cents) per gallon to pump, heat, and centrifuge 275 gallons at a time, which is really just my electricity usage.
I planned to refill before I had gotten to the 2000 mile mark, simply because I figured fuelly was setup to not accept mileage over 3 digits long in a single fuel up. if 1700 miles is the current cutoff, I'll make it a point to fill up before I hit that.