My kids have this but doesnt usually last that long. I think it says 3days but i never go by things like that. Give it a good shake, look at it, smell it, taste if they seem ok id usually go ahead and have it. (But thats me i no others will think differently) the date is for unopened oat drink as it steerile in it carton till u open it.
Just looked on my box of original oatly drink and its says 'storage: opened package stays fresh for at least 5 days in the refrigerator.' So they only giving guidlines no deffinate date
I know this is a few days old now but I've never known non-dairy milks to go bad when opened for a while in the fridge, I've had Oatly chocolate open for a couple of weeks and it's been fine - there's nothing in it to go bad