That's not true
Here is an example:
8÷2x4
PEMDAS: 8÷2x4 = 8÷8 = 1
PEDMAS: 8÷2x4 = 4x4 = 16
PE M|D A|S: 8÷2x4 = 4x4 = 16
And thats not even getting into juxtaposition operations, where fields like physics use conventions that differ from most other field.
but you're missing the point. It could be SAMDEP and math would still work, you'd just rearrange the equation. Just like with prefix or postfix notation. The rules don't change, just the notation conventions change. But you need to agree on the notation conventions to reach the same answer.