B737 FLT CREW OPERATES AN ACFT WITH AN OUT OF DATE NAV DATABASE. MAINT UPDATES DATABASE DURING THE LAYOVER.

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FLEW ACFT VMC BOI-SLC-LAS. ON ARR AT GATE IN LAS; MECH CAME TO COCKPIT WITH NAV DATA. I BELIEVED THE DATA WAS CURRENT BECAUSE I DID NOT OBSERVE THE MECH LOAD ANY NEW DATA. HOWEVER; I HAD TO LEAVE THE COCKPIT FOR A FEW MINS TO TALK TO DISPATCH AND DUTY CTL CONCERNING A SPD BRAKE DISCREPANCY THAT I WROTE UP. SEVERAL LAS MECHS CAME IN AND OUT OF THE COCKPIT WHILE WE WERE ON THE GND. I WAS FORCED TO STAND OUT OF THE COCKPIT WHILE THE MECHS CHKED OUT AND LOCKED OUT THE #1 ENG THRUST REVERSER. NO LAS MECH ADVISED ME THAT THE NAV DATA WAS OUT OF DATE OR THAT HE HAD RELOADED ANY NAV DATA. I DID NOT OBSERVE ANYONE CONNECT THE NAV DATA LOADER. MY FO IS VERY CONSERVATIVE AND I BELIEVED HE CHKED THE DATA IN BOI AND THAT IT WAS CURRENT. I CANNOT 100% ATTEST TO THIS; HOWEVER; I TRUST ALL MY FO'S TO CHK THIS PRIOR TO EACH ORIGINATING FLT. I HAVE NEVER HAD AN OCCURRENCE WHERE MAINT LET ANY ACFT NAV DATA GO OUT OF DATE IN THE PAST; NOR HAVE I EVER HAD AN FO POINT OUT TO ME THAT THE NAV DATA WAS OUT OF DATE.