What is the method for calculating the zakat on a sum of (4276.121) Bahraini Dinars that has not completed a full year? Is the price of gold multiplied by 85 to determine the nisab? Is zakat obligatory on shares when it is unknown whether the company pays zakat on them or not? What about the zakat on the wealth of a deceased father that was not paid before its distribution?

What you mentioned is the method for calculating the nisab (definition), which is the threshold at which Zakat (definition) becomes obligatory. The nisab is a condition for the obligation of Zakat. Zakat becomes obligatory on all wealth when it reaches the nisab and a full lunar year (hawl) has passed over it. Zakat is obligatory on each heir, individually, for their share if it reaches the nisab on its own, or by combining it with other wealth they possess, and a full year has passed over it. The amount of wealth at the end of each year is considered for Zakat calculation. However, if the wealth did not reach the nisab throughout the past years, or if it reached it in some years but not others, then Zakat is obligatory only for the years in which it reached the nisab.