Any reference for the variance on them? I doubt it's too big but would prefer to just see what this is based on.
‘A study published in 2017 tested 31 different melatonin supplements purchased from pharmacies and grocery stores. For most of the supplements tested, the amount of melatonin in the product did not match what was listed on the label.”’
Melatonin Natural Health Products and Supplements: Presence of Serotonin and Significant Variability of Melatonin Content https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5263083/
It also suggests the biggest variance was in mixed-supplement pills while pure melatonin pills were mostly within the normal range. Definitely good to know but I wouldn't worry too much if you are just getting basic pure melatonin from a well-known manufacturer.