"Holland is a coastal state. Could it, on that basis, claim out west of Ireland?"
Not when the UK and Norway have agreed to their boundary meeting in the middle of the N Sea
Way back in the 50's the Brits, Norwegians, Danes and the Netherlands carved up the N Sea and issued oil exploration licences - I think the Germans were sleeping as they were left a small triangle of water offshore Hamburg not extending to the UK line (which was pretty much halfway across the N Sea).
The Danes promptly found some oil fields - the Germans woke up and screamed bloody blue murder as on any "reasonable" definition the fields would have been in German waters. After a few years of arguing the Netherlands and the Danes agreed to a corridor extending German waters to the UK line but the boundary dodged around, leaving the oil fileds in Danish waters
Someone told me that the UK boundary is still not agreed with France & Belgium in the Channel/Straits of Dover area and there are still issues as to where the boundary runs between Eire and the boundary offshore N Ireland for a few miles from the beach.....