**A specific parameter might correspond to a specific (SI) unit, but not all units correspond to a specific parameter**! 

*Kinetic* energy is

$$K=\frac{1}{2} mv^2$$
$$Joules=\frac{1}{2} kilograms*meters^2/seconds^2$$

We also have *gravitational potential* energy:

$$U=mgh$$
$$Joules =kilograms *(meters/seconds^2)*meters\\=kilograms *meters^2/seconds^2$$

So, is Joules both $\frac{1}{2} kilograms*meters^2/seconds^2$ **and** $ kilograms*meters^2/seconds^2$ at the same time? If you have a value in Joules and you need to find the number of kilograms, then how would you go backwards? How would you do the algebra? 

The problem is that there are many kinds of energy with the same unit. In general, parameters have unique units, but units don't belong to unique parameters. You cannot go "backwards" from the unit formulation of a formula.