Dave - are you using fresh herbs in the herbs de Provence, or are they a dried mix, as is typically sold?
You make reference to garlic granules - same question - fresh or dried garlic?
I use dried HdeP. I buy them in small quantities at a time from a Lady who comes to the local markets. She has the turnover to insure that they are reasonably fresh. She sells an amazing range of herbs, spices and herbal cures.
The garlic granules are also dried. These I buy from the Hypermarket. I use them a lot so my supply never goes stale. How fresh they are from the store is anybody's guess.
For the salad dressing you can use fresh garlic if you are making a small quantity and will be using it quickly. It doesn't keep that long. I prefer to make a large batch using the granules as then the dressing will keep longer.
I can't tell the difference in taste.