If you put it to the test you would be very hard pressed to find and identifiable difference, just like wine experts can't tell a 5$ wine from a 500$ wine

Now we're shifting goalposts. No longer about the combination of local conditions/local expertise/local ingredients resulting in a unique product, but about if you'll be able to tell them apart.

So is the weather the same year after year? does that impact it - can we say, tell producers that the weather varied from the day we established the standard so that it can't be called that this year?

Yes it does, as locals know how to control e.g. drying of iberico, or cheese curing, as they've been doing for hundreds of years, with just basic construction techniques (most of the time meaning open buildings, or basic caves). And they can do that because, minor variations aside, local weather remains the same.