Your nose knows. Basically if it still looks pretty white and smells fresh and of coconuts then it's probably ok and taking a taste if it's sour it's off. Of course there's always the adage of, when in doubt, throw it out. Plus coconut milk is pretty cheap.
I hadn't seen this previously sorry.
Some of the tricks I have learnt over the years are to 1 buy coconut cream, not milk and use less it's cheaper in the long run, why pay for the water? (the brand I get, water is literally the only difference between the two)
And 2 buy the biggest tin/can.
Too avoid waste, I'll then decant into smaller containers with a lid into volumes I normally use such as 100ml and
freeze it. It doesn't need to be defrosted to be used because normally I'm putting it into something hot anyway. I have dedicated coloured small containers that are about 150ml in volume that are freezer proof (cost about the same as 1 can of coconut cream) .