Thanks for the info Pipemma but the joy of sailing used to be the relative absence of bureaucracy and rules, especially in Greece. The TEPAI is unbelievably and unnecessarily complicated. It's enough to make me consider leaving Greece and base my boat elsewhere! What a shame.
The YBW forum have been discussing this for a while and various reports of the need for an agent to file out of use papers. One person had a letter from his yard giving details of a local agent he'd need to pay in order to prove his vessel was out of use. He was more than a little annoyed as the yard were effectively asking him to pay someone to prove his boat was in their yard.
However, someone from CA spread some happiness and said that there would be an announcement about a delay. He said that there should be an announcement tomorrow to say the tax is delayed until 2nd May 2019.
I'll be watching for any announcements by Greek government. I already sent them a query about a Brexit related matter and it took about a month to get a reply stating they would look into it. I won't be surprised if the TEPAI announcement takes longer than expected.