I got several coins so worn the lettering &date is not even legible, way more ware than the 71, and all weigh at least 3 grams?
Wear removes the high point details, and yes you can wear away a lot of the details and still be within the weight tolerance. Acid soaking though attacks all surfaces roughly and the coin can be reduced to near paper thinness and still have most all its details. One key indicator on you coin are the rims. Since the acid attacks all surfaces that includes the edge reducing the diameter of the coin. The result is that as the acid works the rim gets thinner and thinner.