collationMatchesDefault seems only read by a few places and all related to timeseries:

• $_internalUnpackBucket
• checkComparisonPredicateEligibility (bucket_level_comparison_predicate_generator.cpp)

However, not all the places set this attribute. For example, find_cmd.cpp does not set collationMatchesDefault, while ParsedUpdate and aggregate do. We need to investigate if this is a bug that find_cmd should have set it, or if this is a deadcode that we can remove.