Backup version compatability

Hi Techies,

I have an netbackup setup where master is running at 7.5.0.4 and most of the medias are running with 7.5.0.7.

I know versions are should be at par with master and backups are running fine with this setup. How this is possible.

1. Is this version level are just symantec recommended or is there any impact?

2. On what basis symantec is saying the versions should be at par with master?

3. What would happen if client version is higher or equal to media server?

Thanks!