Frisians

You could read this as (a) the Frisians were a major group in the 6th century and had become much less important by the time Bede was writng, or (b) Procopius' informant happened to know about Angles and Frisians, and Bede's sources happened to know about Angles, Saxons and Jutes, neither list being necessarily complete, or (c) the names could be applied imprecisely and inconsistently (by analogy with modern ethnic labels like 'Asian').

Lord of Silver, by Alan Fisk. Book review Carla 2008

The Frisians were the only ones to retain their national peculiarities after losing their national independence.

The Catholic Encyclopedia, Volume 13: Revelation-Stock 1840-1916 1913

It is claimed that the Frisians were the first Europeans to smoke pipes.

A Wanderer in Holland 1903

He rides on his white horse along his dike and feels himself to be "at the center of all the Frisians alive and dead .... [towering] above them all."

From the editor 2009

He rides on his white horse along his dike and feels himself to be "at the center of all the Frisians alive and dead .... [towering] above them all."

A Different Stripe: 2009

Agard's country was neighbour to the Frisians, and a sad, flat country of fog and fen it was.

Chapter 17 2010

Frisians by mischance, in a two days 'hunt, ran me down.

Chapter 17 2010

He rides on his white horse along his dike and feels himself to be "at the center of all the Frisians alive and dead .... [towering] above them all."

Translation 2010

He rides on his white horse along his dike and feels himself to be "at the center of all the Frisians alive and dead .... [towering] above them all."

Deals 2010

All around it, they had infographics showing how many nukes the Frisians had, how they expanded their territory after a series of attacks from the Dutch and from the other countries, how much (military) aid they were getting from the US, how much the Frisians (in this hypothetical) had suffered in their genocide, etc.

The Volokh Conspiracy » Let Turkey Have Gaza 2010