Do you really need this fine print? It sounds like this fine print about only using timer data points would only be helpful if you were (a) dishonest enough to enter fake data points, BUT (b) honest enough to abide by the fine print! It sounds like (b) is true since you are apparently willing to redo goals just because of your fine print. So are you really worried about (a)? If you are willing to abide by the fine print, why not just make the fine print say "no fake data points"?
Personally, I do this quite often (start doing a task but forget to start the timer). As soon as I realize it, I typically (1) estimate the amount of time I have already spent and enter a data point, and then (2) start the timer. I always try to estimate (1) as accurately as I can; I don't find myself tempted to report inflated estimates. Over the long run, it probably all averages out. Ideally, of course, I would always remember to start the timer---and I do try to remember---but realistically, there will always be times when I forget. In fact, the times when I forget are often the times when I am being so productive/in the flow that I really *want* to do the goal, or I have made the goal an automatic habit, and I just get right on to doing it without remembering that I am supposed to track it! That being the case, it seems particularly silly to penalize myself by saying the work I did without the timer running doesn't count, because I want to *encourage* this sort of behavior.If you are really worried about this, however, it is exactly what TagTime is designed for: http://messymatters.com/tagtime/ . You never have to worry about remembering to start a timer, in exchange for a loss of precision in measuring the amount of time spent doing any particular thing. I find it works well for big goals, like spending 40 hours/week on work, or 10 hours/week on reading or research or studying, but it doesn't work well for smaller goals like spending 30 minutes or 1 hour per week doing something, because the variation is just too high. (You could have TagTime ping you more frequently to get a higher resolution, but that just starts to get annoying and disruptive.)