Your usage of the term 'feedstock' here is confusing, and it seems like you're probably operating under the erroneous assumption that contract manufacturer supplies commissioned by Novo Nordisk are somehow being routed to compounding pharmacies, which isn't the case.

In practice, there are generic manufacturers for semaglutide, and many other peptides still protected by US patents, mostly located in China. The more reputable of these manufacturers produce these drugs at levels of purity rivaling the 'name brand'. These manufacturers export lyophilized product en masse to middlemen that operate in the grey/black-market 'research chemical' sales market, or ship to compounding pharmacies. The consumers purchasing on the grey/black market reconstitute the drug at home (which requires a trivial level of effort), and assume some extra degree of risk in terms of product purity and sterility. Consumers wanting an extra level of assurance for product quality purchase from a compounding pharmacy that ostensibly is conducting its own assessments of product purity, and following best practices for sterile reconstitution.