ACR CREW CONCERNED THAT THEY MAY HAVE CROSSED AN APCH FIX 1000 FT TOO LOW AT MIA; FL.

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A FLT FROM TPA-MIA APPROX XA00; CLR AND 10 DME. BEING VECTORED BEHIND AN ACR SAAB FOR AN ILS APCH TO MIA RWY 27R. ON BASE LEG IN A DSCNT FOR 3000 FT; WE WERE GIVEN APCH CLRNC AND TOLD TO CROSS BASHO AT 3000 FT; I BELIEVE. NOTICED BASHO NOT ON OUR DISPLAYS. I FOUND IT ON THE APCH PLATE AND SAID WE COULD IDENT IT BY 10.9 DME. CAPT ADDED BASHO TO OUR APCH ON THE FMC. AFTER THE DISTR; WE COULD NOT REMEMBER IF WE HAD BEEN CLRED TO CROSS BASHO AT 2000 FT OR 3000 FT. CAPT THOUGHT 2000 FT; I THOUGHT 3000 FT. I THINK WE SETTLED ON 2000 FT; PICKED UP THE GLIDE PATH AND VASI'S; SWITCHED TO TWR; AND DIDN'T THINK ANYTHING MORE ABOUT IT. TODAY; I WAS THINKING ABOUT IT AND CANNOT RECALL IF WE CONTINUED OUR DSCNT TO 2000 FT OR STOPPED AT 3000 FT. THIS WAS THE 4TH LEG OF A VERY LONG DAY (8 HR FLT TIME; 12 HRS ON DUTY). WE WERE BOTH PRETTY TIRED; AND IT IS POSSIBLE THAT WE MADE A MISTAKE ON THE ALT. SUPPLEMENTAL INFO FROM ACN 469950: NEXT DAY; DISCUSSION WITH MY FO ON THIS PROMPTED THE DECISION TO FILE THIS RPT. THIS WAS THE 4TH OF A 4 LEG DAY AFTER BEING AWAKE 15 HRS. IT IS POSSIBLE A MISTAKE WAS MADE ON THE ALT. I HONESTLY DON'T KNOW AND AM NOT ABLE TO RECALL THE EVENTS WITH MORE DETAIL. TWR DID NOT QUESTION OUR ALT. IT IS POSSIBLE WE WERE CLRED TO 2000 FT AND WENT THERE. OR WE COULD HAVE GONE TO 2000 FT WHEN CLRED TO 3000 FT. I JUST DON'T RECALL. WHAT BOTHERS ME IS I DO REMEMBER THE FO QUESTIONING THE ALT AND THAT I CONFIRMED WHAT I UNDERSTOOD TO BE CORRECT. I THOUGHT ALL WAS UNDERSTOOD. I DID NOT JUST CHK WITH ATC; WHICH IS WHAT I WOULD NORMALLY DO ANY TIME THERE IS A QUESTION ABOUT A CLRNC. I HAVE TO WONDER HOW MUCH THE LONG DAY COULD HAVE FACTORED INTO ALL THIS. FRANKLY; I AM SURPRISED AT MY LACK OF RECALL OF THE EVENTS BUT FIND MYSELF STILL TIRED AFTER A NIGHT'S REST.