as per https://issues.apache.org/jira/browse/CASSANDRA-3724 and subsequently https://issues.apache.org/jira/browse/CASSANDRA-3657. It is allowed behavior to have less items in a composite column than the composite type specifies.
for example, given a column with type CompositeType(UUIDType,UTF8Type), a column specifying only the uuid portion is considered valid. This would serialize to where eoc is the last byte of the first composite portion.
Handle reading composites with prefix of components