Rounding errors will cause them to keep 0.1 trade power in Lübeck. Whether this 0.1 trade power is enough to drag forward 20% of the node's value is dependant on various factors such as Dutch trade steering capability, other countries possessing trade power in Lübeck, and much more.
The most likely situation though however is that while other countries have trade power there too, the Netherlands are the only country steering trade in Lübeck. To quote the wiki,
If only one country is steering, all trade leaving the node goes to the node that country selected, no matter how tiny their trade power is.
Let's say hypothetically only three countries have trade power in Lübeck. Germany (you), the Netherlands, and Britain – you have 75% of the trade power, the Dutch have 1%, and the Brits have 24%. Even if Britain doesn't have a merchant in Lübeck actively diverting trade towards EC, their 24% would still affect the amount of trade value leaving Lübeck if the Netherlands were steering trade towards EC, meaning you would lose a total of 25% trade value. Either annex the Dutch, or remove all other countries with trade power in Lübeck and EC.