Many years ago I was working for a haulage company whose charts where checked by the ministry. No problem was found, but they ask that we put a line across the charts and mark it with edr and sdr or ewr and swr. I have done this and have been stopped for tacho checks on several occasions without problems, but I agree it is not a legal requirement, but if it keeps the ministry happy what’s the harm.
However how can we comply by the law when the rules aren’t interpreted the same across Europe?
A bit late in the day I know, but 
(week ago, I kept forgetting when I was sat here). As Niel is getting company infrigement sheets with this business highlighted. Its so they only have to scan one side of the disc to get all the details of his complete working day, possibly for pay reasons (paid for what is on the disc). Just a thought.