it’s like giving Fentanyl to someone expecting Oxycodone.
Doing that (without adjusting the dose) would likely kill them because difference in potency (and LD50) is absolutely massive. The difference in potency between Desoxyn and Adderall exists, but it's way, way, way smaller than that. In terms of the riskiness of drugs that may be "laced" with their more-potent counterpart, they aren't even slightly comparable.
Nobody's going to OD and die because they accidentally got some Desoxyn in their Adderall.