Yes, but they tend to be minor and inconsequential to most projects. Experienced asphalt crews will often notice small differences in the workability of asphalt mixes, subtle variations in oil content, and concentration of large and fine aggregates (called gradations). However, most plants produce hundreds if not thousands of tons of asphalt each day, so they must monitor quality closely to protect their own interests. Virtually all modern plants are computer controlled and oil content and gradations meet rigid quality control standards, often to CalTrans (in CA anyhow) standards.  There is always an acceptable range for oil content and gradations. Some producers shoot for the lower end of the acceptable range as a means of reducing costs while others prefer to be safely in the middle. For parking lots and low volume roadways, the quality of materials is likely to be comparable regardless of which producer supplies the material. With asphalt, the quality of the placement and compaction has a much larger impact on quality and longevity than the small variations in the material.