Interesting that they don't have stats on amphetamines which is the same derivative as meth but is a different but more dangerous end product.
https://www.thecabinchiangmai.com/the-difference-between-methamphetamine-and-amphetamine/
Despite the 'official' criteria for designating a serial killer being 3, I believe 2 unrelated with similar MO should trigger a SK response and the ones that survive added in the number until proven to be unrelated crimes.
Edit------ should have read 'which is a different but more dangerous end product'