I understand the rule but I'm unaware of the parameters and criterias for giving probability. Like in China there are some muslims and in Brazil also there are Muslims. So is that a parameter to give the probability and how much percentage we have to be sure for giving probability?

Substantial means that the origin country /disembark country may produce halal leather and one cannot exempt the possibility of being paak leather. There are some places /counties you can not say that there is no chance of being halal like India. I mean if the leather has been imported from Kerlala, Tamil nado then there is probability of being halal but if it's from China then despite a percentage of Muslim population it's very hard to get satisfaction of being zabeehaa.