However the difference is when the savings are not merely savings but an investment though still existing in monetary form. In the other thread about the 401K, the difference between the 401K savings and regular saving of wealth is that the 401K wealth is not merely savings, it is an active investment which is subject to profit and loss. Let me give an example, zakat is levied on produce but not on the land itself which is being used for growing the produce. The produce is actually the income earned from the land (which is an investment to say). So savings which are actually investments are similar, the dividends you get are the income.
If I have savings that are idle and not invested, then I agree it is subject to zakat ul maal. Centuries ago there was no form of investment in which money remained in monetary form and still could grow, investment had to be bartered in the form of trade goods.
I am looking for a parable where your savings is your earning and zakat is levied on it. So far I have found none in historical context.
My original question is still unanswered as well. None of the texts indicate the wealth on which zakat has been paid needs to be paid again unless it is new wealth.
Just so you know my own stance, I pay zakat yearly irrespective of whether I have paid on it before. This I do out of spiritual obligation but not out of the rationale that is prevalent today. I do not agree with it because it so far has no founded bases and that is what I am seeking by playing the devils adovcate here. What I am stating here is not what I actually do in real life. But we should objectively think about the rationales that are presented to us and see if they are in line with the texts we have.