Is it obligatory to pay the zakat on gold for past years, concerning which there is doubt about the method of calculation, in addition to the zakat for the current year, in order to absolve the deceased?

As long as the deceased used to pay Zakat (definition), the original presumption is that her financial obligations are cleared. The doubt of the heirs does not negate this original presumption, because the fundamental principle regarding a Muslim's acts of worship is their validity and sufficiency until proven otherwise. Therefore, the heirs are not required to pay Zakat on jewelry for past years. If they wish to give charity on her behalf, the reward will reach her, Allah willing.