Commercial Fixed Wing
Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Communication Breakdown; Confusion; Situational Awareness
Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
General None Reported / Taken
Environment - Non Weather Related; Human Factors; Procedure
Our flight clearance to ZZZ ended with ZZZZZ [Intersection] ZZZZZX [Arrival] which is the arrival for ZZZ landing direction. I confirmed all crossing altitudes and speeds were in the FMC.  We had ATIS automatic updates and received information just prior to the start of the descent confirming ZZZ landing direction.  Prior to descent; we briefed the various expected taxi routes from the possible runways; flap setting; landing assessment; and autobrakes.  We held off on briefing the ILS pending the runway assignment.  At some point we were cleared for the ZZZZZY Arrival but then given various headings; speeds and altitudes for spacing before clearing us direct to ZZZZZ1 [Intersection].  At that point; I believed the ZZZZZY Arrival was the name of the arrival we had in the FMC and I still expected to land direction. As we crossed  ZZZZZ1; ATC told us to depart ZZZZZ2 [Intersection] heading 300.  ZZZZZ2 is not on the STAR we had in the FMC. That is when we realized we did not have the ZZZZZY Arrival in the FMC.  The routing prior to ZZZZZ1 is the same on both STARs.  The Captain selected the STAR in the FMC and we flew the route.  ATC continued to directed speed and altitude.  We were never off route.  I'm not certain but I don't think we were ever off altitude because ATC was assigning us incremental altitudes the entire descent.  Confirmation bias was one causal factor for me.  I had a flight clearance; current ATIS; and waypoints in the FMC that coincided with the arrival clearance.  After various vectors; ATC cleared us to a point that was six waypoints into the arrival; a point with the same name as the new arrival; and it didn't occur to me that the arrival had changed.  My currency and recency was another causal factor. I completed IOE; but didn't consolidate before starting a six month leave of absence.  The Captain was exceptionally helpful and specifically stated in the departure brief that me not speaking up for any reason was his biggest concern.  I wanted to brief the approach during the initial descent to stay as far ahead as possible.  He suggested we hold off since we didn't know the runway yet.  I wanted to ask approach for an expected runway; but I assumed that he didn't want to do that because he flew into ZZZ enough to know when they usually give you the runway.  That was a moment to speak up. Requesting the expected runway at that point would have clued us in to the change of runways and change of STARs.I will confirm the STAR with the other pilot the same way I confirm an approach; altitude or landing runway; e.g.; I heard cleared for the ZZZZZY or descent via the ZZZZZY.
Air carrier First Officer reported confusion on which intersections they should be going to on the STAR during descent.