someone please make my below confusion clear

how do you know if your package reached in TSC(texas service center) without getting the receipt ? employer usually send the package to dallas lockbox (if you are from east coat) or phoenix lockbox (if you are from west coast) from where uscis routes the package to either nebraska service center or texas service center, isn't it? if this is the case you have no control to send your package to NSC or TSC .

that is what my understanding was, please help make it clear.