I'm with Xtreem on this. Sober days before a relapse aren't "lost"--you had them, and hopefully you learned from them things that will support your future sobriety. But knowing my own propensity for rationalization, to resume the counting from where I left off would be just another bit of denial and dishonesty with myself. It also would be misleading to others who might be deprived of the benefit of my experience with the relapse.
I know people who have had to restart the clock after 10 or 15 years of sobriety. They were very brave, and I respected their honesty.