Is there such a thing as a therapeutic grade essential oil?

The sort answer is simply "No".

The terms 'therapeutic grade' or 'clinical grade' is a marketing fabrication and doesn't mean anything. Why would a pure and natural lavender oil made from distiller A be more 'therapeutic' than a pure and natural lavender oil from distiller B in the same village?

It's important to consider two factors:

1) The various aromatic compounds that constitute an essential oil always vary a from batch to batch and from crop to crop. This is due to many factors:  the varietal, health and maturity of the plant, the weather condition that year, the harvesting method, the distillation equipment and sometimes method, the know how of the distiller, etc. All these factors will affect the quality and smell of the oil in the end to a certain degree. 

2) For a specific lavender oil from a specific producer to be considered 'therapeutic', you would have to have very long, thorough and expensive medical scientific studies that test the potency of that oil against various  ailments. And what then when the next batch is slightly different? Should it be tested also? And why would that oil be more therapeutic that the oil produced by the neighbour? Was it tested against it?

In reality this never happens simply because it is impossible to implement.

Some better questions that one should ask about essential oils are:

- Is your essential oil pure and natural?

- What is the botanical specie (and when applicable varietal)

- What is the country/region of origin?

- How is it distilled? Water? Steam? 

- Is it whole, rectified, fractionated, etc?

It is only when you have this information that you can truly compare the quality between two oils. See more about quality here.