My understanding is that all hemp is cannabis. I think the common understanding is that cannabis derived terpenes are more sought after than non-cannabis derived blends. One exception is ‘flavorless’ terpenes which are used to adjust viscosity. Within the cannabis derived terpene sphere there are multiple subcategories. Cultivar (aka strain) specific terpenes are most desired, with ‘marijauana’ strain specific terpenes being the most rare. Hemp derived, cultivar specific terps offer a similar profile, though marijauana derived terms are more rare and cultivar specific ones are typically from a smaller, more homogeneous batch. This is due to the fact that cultivars are more stable in the marijauana realm because cloning is so commonplace. Most hemp derived terpenes, even cultivar specific, have more variability due to phenotypic variation. This is pretty standard in hemp because it is mostly from seed & the seed is overall not super stable. This is changing rapidly, but I think that the vast majority of hemp grown for the 2018 crop had some substantial characteristic variation. Overall,only the hemp from clones had perfectly stable characteristics. Marijauana derived terpenes fetch a premium due to smaller crops and more phenotypic stability. Steam distilled hemp terpenes can be of high quality as well, though fetch a lower price due to crop size & cultivar variation.
Terpene quality is directly related to processing style. My experience is that steam distillation of fresh flowers gives the highest quality terpenes. This is the industry standard for botanical essential oil extraction across the board (lavender, mint etc.) It is possible to distill fresh cannabis material & then dry it and extract the cannabinoids. This presents the obvious challenge of drying it first, but totally possible. My limited research shows that steam distillation seems to degrade the cannabinoids, somewhere around 25%. Distillation of dried flower appears to most commonly be done by fractionating cryo-ethanol crude during the process of post-processing distillation. My limited expirrence with this style of terpene collection has shown it’s totally possible and requires a skilled extractor to pull off well. It’s also worth considering the volatility of terpenes and the changes that typically happen during the drying process. The lightest terps often transform when exposed to the atmospheric conditions, especially heat.