DC10 FLC FAILED TO RECEIVE LNDG CLRNC PRIOR TO TOUCHDOWN. APCH CTLR FREQ CONGESTION LED TO LATE HDOF AT CREW'S PROMPTING.

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OUR FLT WAS HANDED OVER TO SEATTLE APCH. AFTER VECTORS TO INTERCEPT THE LOC; SEA APCH CLRED US FOR THE APCH; ILS RWY 16R. WE WERE TOLD TO MAINTAIN 170 KTS (I BELIEVE IT WAS) UNTIL THE MARKER (PARKK). I WAS THE PF AND IT SEEMED TO US THAT APCH CTL WAS ALSO HANDLING THE TWR ON THE SAME FREQ; AS WE DIDN'T HEAR APCH ADVISE ANY TFC TO SWITCH TO TWR AT PARKK. FROM PARKK INBOUND WE WAITED FOR APCH CTL TO HAND US OFF TO TWR OR CLR US TO LAND. AT APPROX 2 1/2 MI OUT THE CAPT ATTEMPTED TO CONTACT SEA APCH; HOWEVER; DUE TO OTHER TFC COMS WITH APCH; HE WAS 'STEPPED ON.' THIS WAS REPEATED A COUPLE OF TIMES UNTIL CONTACT WAS MADE WITH APCH OVER THE 'RAIL' SHORT (VERY) FINAL. SEATTLE APCH WAS ASKED IF WE WERE CLRED TO LAND?! AFTER A MOMENT; APCH SAID 'CONTACT THE TWR.' AT THIS POINT I HAD BEGUN TO FLARE THE DC10 AND THE CAPT CONTACTED THE TWR AS WE TOUCHED DOWN. TWR ADVISED US TO ROLL TO THE END AND CLRED US TO CROSS RWY 16L; TAXI TO PARKING ON THIS TWR FREQ; NO COMMENT WAS MADE. VISIBILITY WAS GOOD AND WE COULD SEE THAT THE RWY WAS CLR OF OTHER ACFT (LNDG AND DEPARTING). WITH GND AND TWR FREQS AND TWR AND DEP FREQS COMBINED AT SOME ARPTS AT LATE HRS; APCH AND TWR DOESN'T SEEM UNREASONABLE.