Not true. It is properly filed as long as it's received before the I-94 expires.You have to file I-539 45 days before your I-94 expires.
I know the instructions suggest you file 45 days before. But you said "you have to", which is not true. And I do not see any real difference between filing 45 days before compared to less than 45 days before.In the I-539 instruction, Page One:
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