回复：急问PIJIANG, 863211, 我能否到USCIS取一个要求补件的回信信封？

You must have that RFE letter with barcode. Otherwise you won't ever see the online message, "your response received, case resumed"
However even without barcode, without that online confirm message, your response still will reach the IO in time (or considered as responded in time) if you clearly mark essential information and keep the tracking/delivery evidence.