Which means there is a slight excess of both potassium

Question

28 KClO₃ (s) + 6 Sb₂S₃ (s) + 3P₄ (s) -> 28 KCl (s) + 3 P₄O₁₀(s) + 6 Sb₂O₃ (s) + 18 SO₂ (g)

The actual reaction mixture is 63% KClO₃, 31%Sb₂S₃, and 6% P₄, which means there is a slight excess of both potassium chlorate and phosphorus. On the basis of the stoichiometry presented, the reaction mixture should be 58.7% KClO₃, 34.9%Sb₂S₃, and 6.4% P₄. Why is an excess of both phosphorus and potassium chlorate present in the reaction mixture?