When dealing with concentrated chemicals, the results desired are directly related to the concentration used. With sodium chlorite the goal is to end up with a concentration that is used for a specific purpose.
Since sodium chlorite comes in many concentrations, we look at the concentration of the ending solution. Since only small amounts are needed for most applications, we deal in Parts Per Million.
Drops as a measurement are not all that accurate. It takes practice to form a "standard" drop, and then the amount in the drop varies depending upon the size of the hole in the dropper and the concentration of the chemical. MMS
presents a particularly difficult situation because you are using a highly concentrated sodium chlorite mixture and only mixing a half a cup of solution. It is more repeatable to measure in ml or cc and dilute the concentration of the chemical to allow for standard measurements.
If PPM is confusing for you, perhaps you can think in terms of %. For example with hydrogen peroxide you may start with 35% (which is 350000 PPM) and you want to dilute it down to a base solution of 3% (30000 PPM). From there you dilute as needed for your applications.
With MMS you are starting with 224000 PPM or 22.4%. The Lubbers study showing no adverse effects was done with 5 PPM or 0.0005%.
Long term water storage utilizes the preserving properties of sodium chlorite. Taking water that has been purified, you add enough sodium chlorite to end up with a concentration of 6 PPM. When stored in a cool area away from UV light, this water will keep for around 5 years.
When activating sodium chlorite with water you are entering into the area of "stabilized oxygen" products. The "usual" dose recommended is in the 20 - 50 PPM range. In comparison, your 5 drops of MMS in 3 liters of water gives you a concentration of around 22 PPM or 0.0022%.