In addition to what has been said above, you can calculate the concentrations of the previous batches present in the current bread starter. For example:
Bread starter 100 kg --> Composition, let's say 80 kg flour batch 1 + 20 kg water
If you always replenish when there is 20 kg remaining Bread starter, you know this is composed of 16 kg of flour batch 1 + 4 kg water
You will need to add 64 kg of flour batch 2 and 16 kg water to have a new 100 kg
This new 100 kg is composed of:
64 kg flour batch 2
16 kg flour batch 1
20 kg water
Next time when there is 20 kg Bread starter left, you know that it's composed of 20 % of the above quantities, so: 12.8 kg flour batch 2, 3.2 kg flour batch 1 and 4 kg water. When you add 64 kg of flour batch 3 and 16 kg water to obtain 100 kg Bread starter, the new 100 kg is composed of:
64 kg flour batch 3
12.8 kg flour batch 2
3.2 kg flour batch 1
20 kg water
By repeating this calculation you will see that at a certain moment, the quantity of flour batch 1 becomes theoretically insignificant in your finished product. It allows you also to calculate the concentration of flour batch X in your finished product.
Another point to add, in the case of batches that are used for such long periods and present in almost all your products, is to be 100 % sure of the quality (GMOs, organic) and the food safety (toxins, micro-organisms, allergens) of the used flour. Any problems with the flour can put your business at risk, it's important to be aware of that.