Opps! I was not aware of this effect!!
I've been investigating it and the duplicated posts (due to re-editing) can reach an average of 30% which has surprised me a lot.
"Fortunately" this effect occurs in all categories. As I had used comparative rates, the results not vary significantly (0.644% the most). Only some categories with very similar values permute their positions in the rankings.
Without a doubt this effect must be taken into account because in other types of analysis the results can vary substantially.
Thanks for showing me this!