The 4x100m relay results are expecting all team members to be the same age division and gender.
The 4x400m relay results allow for mixed age division and gender teams. If a 4x400m relay team is all one gender and age division, the results are uploaded to Athletic.net.
When we run a mixed age division or mixed gender team, the team is marked as "Exhibition" with an "X" so they are not uploaded into Athletic.NET. The relay team still has a time, but it keeps the relay results "pure" in Athletic.NET so we don't upload and "8 & under" boys team that has three 7 years old's and one 18 year old.