EntityValue[EntityClass["Country", "Europe"], {"Name", "Flag"}]

Illustrates the second flag is in-fact for Svalbard.

According to the knowledgebase, the (51) countries in Europe are:

In[3]:= EntityValue[EntityClass["Country", "Europe"], "Name"]
Out[3]= {"Albania", "Andorra", "Austria", "Belarus", "Belgium",  "Bosnia and Herzegovina", "Bulgaria", "Croatia", "Cyprus", "Czech Republic", "Denmark", "Estonia", "Faroe Islands", "Finland",    "France", "Germany", "Gibraltar", "Greece", "Guernsey", "Hungary", "Iceland", "Ireland", "Isle of Man", "Italy", "Jersey", "Kosovo", "Latvia", "Liechtenstein", "Lithuania", "Luxembourg", "North Macedonia", "Malta", "Moldova", "Monaco", "Montenegro", "Netherlands", "Norway", "Poland", "Portugal", "Romania", "San Marino", "Serbia", "Slovakia", "Slovenia", "Spain", "Svalbard", "Sweden", "Switzerland", "Ukraine", "United Kingdom", "Vatican City"}

Unfortunately, this does not return the appropriate source:

EntityValue[Entity["GeographicRegion","Europe"],"Countries","Source"]

but judging from this:

In[6]:= EntityValue[EntityClass["Country", "Europe"], "Flag", "Source"]
Out[6]= {"CIAFactbook"}

I'd say the CIA World Factbook is a good bet, which indeed includes Svalbard. Hope this helps.