According to USBC rules:
Absentee score vs. vacancy score the first night
If a
bowler is not present the first week of bowling, which score should the
bowler receive the first night – an absentee score or a vacancy score?
Unless
the league has a rule to state otherwise, or a past practice has been
established within the league, the league absentee score is used (Rule
105). If there is any question as to whether the bowler is on the team
roster or what score should be used, the league board of directors (the
team captains and officers) decides by majority vote.