This is partially true.
If you never receive the first notice, but then get approval notice for I-751 in the mail... Then you can apply for N-400 with copy of approved I-751. But of course, if you don't have a notice for I-751, and you apply when it's pending, it can be problematic if USCIS asks for it.
But again, if you missed I-751 notice and letter containing code for your account, then you might as well miss any other upcoming notices (biometrics, RFE, interview or approval).