We do remove old money: the outputs of 160 years old transactions is purely and simply non-usable. So in the nodes database, the sources of this age are removed.
Now, how do we identify the sources to remove? The UnitBase could be very helpful.
Indeed, the UnitBase increments every 23 years approximately (the monetary mass $M$ grows by 10 times every 23 years with c = 10% as you know). We deduce from this that, passed exactly 160 years, $M$ has grown by $10^{160 / 23} = 10^{6,95}$ times.
So we can consider $7$ incrementations of UnitBase allow us to destroy some money.
For example, let’s say that current UnitBase is 7 and call it CurrentBase. Then any source with UnitBase <= CurrentBase - 7 can be destroyed: the sources refering to UnitBase = 0.
Other example: if CurrentBase is 28, then any source with UnitBase <= 21 can be destroyed.
As a conclusion, we could say that we only keep the last $7$ UnitBase sources, as they are equivalent to money between now and 160 years old.
And a second conclusion, we see that:
- UD is has a max “value” of 999.999 = 10^6
- We have a max number of members around 1 million = 10^6
- We handle at max 7 UnitBase = 10^(7 - 1) (because base 10^0 = 1, so we don’t count it as a power of 10)
So in the end, we have a window of total monetary mass maxed at $10^{3 \times 6} = 10^{18}$. And that’s super cool, because an unsigned integer today can handle a value up to $9 \times 10^{18}$. We are all good 