If we just discussed this as d-amphetamine, l-amphetamine & methyl-amphetamine, the issue of interchangeability would be less confusing.
Talking about methamphetamine as a different molecule is not helpful, as Adderall itself is not a single molecule.
Which I suspect you know, as you mention different enantiomers of thalidomide. However you don't point out that adderall itself is a 3:1 racemic mixture of l and d amphetamine.
The real discussion here is the receptor binding affinity of the various targets of the drugs, and how they compare.
The vast majority of adderall prescriptions are XR.
Enantiomers are structurally “the same molecule” (or people often speak this way depending on the context) but with different optical configurations.
There's a whole section, "Single-Isomer Versus Racemic Formulation", in this recent review article titled "Novel Formulations of ADHD Medications: Stimulant Selection and Management" https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8412159/
The psychiatry handbook of Massachusetts General Hospital also uses racemic in this context https://www.sciencedirect.com/science/article/abs/pii/B97814...
Also, I can't find any data on what percentage of Adderall prescriptions are XR, have you found anything?
Looks like the LRx database would be the place to look from scanning this report for the DEA. https://www.deadiversion.usdoj.gov/pubs/docs/IQVIA_Report_on...
Adderall is normally prescribed in the XR formulation (meaning it's an extended/slow release capsule), and has amphetamine as the active ingredient.
Methamphetamine is a different molecule altogether, and typically it's not packaged in slow-release capsules.
Yes, methamphetamine is structurally related to amphetamine, but you shouldn't make the mistake to think they are interchangeable. Very often the difference between two very similar molecules is the difference between life and death (for a classic example, look up the two enantiomers of thalidomide).