CPR ACFT ENTERS RWY WITHOUT CLRNC AT MIA; FL.

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WE WERE THE ONLY ACFT WAITING FOR OUR TKOF CLRNC ON RWY 9L. LCL CTLR ADVISED AN ACFT ON FINAL THAT A KING AIR WOULD BE DEPARTING PRIOR TO HIS ARR THEN CLRED HIM TO LAND. IMMEDIATELY FOLLOWING THAT; HE CHANGED OUR DEP CLRNC ALT AND HEADING; FOLLOWED BY OUR FO'S READBACK. I WAS CONFIRMING NEW ALT AND HEADING AND BEGAN TO TAXI INTO POS ON RWY. CTLR ADVISED THAT NO POS AND HOLD CLRNC HAD BEEN ISSUED AND INSTRUCTED US TO TAXI CLR OF RWY AND HOLD. AN ACFT LANDED; WE WERE CLRED FOR TKOF AND DEPARTED. 2 THINGS CONTRIBUTED TO MY MISTAKEN 'POS AND HOLD' CLRNC. 1) WHEN I HEARD OF 'A KING AIR GOING TO DEPART PRIOR TO MY ARR' I ASSUMED THAT THIS WAS TO THE #1 ACFT ON FINAL. SO I EXPECTED TO BE ISSUED OUR POS AND HOLD OR TKOF CLRNC NEXT. 2) WHEN GIVEN A CHANGE IN DEP INSTRUCTIONS; THIS IS USUALLY DONE AT THE SAME TIME AS A POS AND HOLD OR TKOF CLRNC. SINCE I HAVE TO ASSUME THAT THE CTLR WAS CORRECT AND HAD NOT CLRED US ONTO THE RWY; I MUST ALSO ASSUME MY ERROR WAS CAUSED BY MY NOT LISTENING CLOSELY ENOUGH AND WAS CONTRIBUTED TO BY THE COMMON PRACTICE OF ISSUING LNDG CLRNCS TO MORE THAN 1 ACFT ON FINAL. I WILL MOST CERTAINLY LISTEN MORE CLOSELY FOR 'THE MAGIC WORDS' IN THE FUTURE. I ALSO BELIEVE THAT ISSUING LNDG CLRNCS TO MULTIPLE ACFT ON THE SAME RWY IS UNNECESSARY AND SHOULD BE SUSPENDED; SINCE IT MAY LEAD TO CONFLICTS OF MANY TYPES.