Redshift not loading sorted data as sorted

Following this doc: https://docs.aws.amazon.com/redshift/latest/dg/vacuum-load-in-sort-key-order.html

It seems that we're loading things according to these guidelines but our data is still defaulting to loading as unsorted. If we're using a time based sort key and there is overlap in this way:

Existing sort keys in table:

1 2 3

New sort keys in COPY:

3 4 5

Would the overlap on the 3 value explain the behavior we're seeing, even if the data could technically be considered sorted?