Something certainly has to be done to make Germany immediately invading the Netherlands and taking their resources less of a no-brainer.
I agree it doesn't feel right. There is an NF to intervene if the fascist party in the Netherlands starts increasing in popularity, so might end up with a coup. But not if fascists invade and annex.
But on 17 January 1940 the Prime Minister said to Parliament:
"The obligations of His Majesty's Government in the United Kingdom in respect of [guarantees by this country of assistance against aggression] relate to the following countries and derive from the following instruments.
§ France.—The Treaty of Locarno of 16th October, 1925 .
§ Belgium.—The Treaty of Locarno of 16th October, 1925 and the Anglo-French Declaration to Belgium of 24th April, 1937.
§ Portugal.—The various Anglo-Portuguese Treaties and Agreements, [going back to the 14th Century].
§ Iraq.—The Anglo-Iraqi Treaty of Alliance of 3oth June, 1930.
§ Egypt.—The Anglo-Egyptian Treaty of Alliance of 26th August, 1936.
§ Greece and Rumania.—My statement in the House on 13th April, 1939.
§ Poland.—The Anglo-Polish Agreement of Mutual Assistance of 25th August, 1939.
§ Turkey.—The Treaty of Mutual Assistance between the United Kingdom, France and Turkey of 19th October, 1939"
Unlike the situation in WW1, there were no secret treaty arrangements, the above list is complete. Though there was in progress secret talks with Norway and Sweden about intervening in the Winter War.
There was no guarantee of the Netherlands. They had been strictly neutral in WW1, and intended to do the same when war broke out. But would that have remained the same if Germany had started creating a CB to justify a war? I doubt it.
Plus internally within Germany, could Hitler have justified a war against a neutral in 1936, where there were no territorial claims? The "punishment" for a German player is only that WT increases.
There was no guarantee of Ireland mentioned by Chamberlain, but the arrangements for Independence of the Republic must have covered this. Ireland couldn't defend itself against aggression. It had the exact same status as other Commonwealth countries at first. The legislation in each case would have covered mutual defence, as an "internal" matter, rather than by International Treaty. As was the case with Canada etc. But by 1939, the Republic preferred not to join the DoW, but remain "neutral", knowing they would be protected. As did Egypt, which didn't even formally issue a DoW when it was invaded.