Whatever your system, keep it on the up and up. Padding your log to produce more impressive figures serves no purpose other than self-delusion. You can tell yourself you’ve been running x number of miles per week all you want, but if you’re consistently getting to x via fuzzy math, what’s the point? Your body will tell you it’s really been less than x, especially when it comes time to race. (Besides, if you can’t be honest with yourself about how much you’ve been running, in what other ways are you deceiving yourself?)
One Olympic marathoner I know specialized in inflating his log. He’d be out with a group on, say, a 10-miler, and say, “Hey, guys, let’s slow it down, I want to get 11 for the day.” That is, he was going to run the same distance, but by making the run take more time, he then allowed himself to count the run as farther. He even claimed in a running magazine that putting down that he’d run 120 miles for a week instead of the 100 he probably ran gave him more confidence. I’ve yet to find anyone else in the fifteen years since he stated this who thought it was a good idea.