The real rules citation for Freeblades:
THE <NOBLE HOUSEHOLD> KEYWORD
Every datasheet in this section has the <NOBLE HOUSEHOLD> keyword. This is a keyword that you can select for yourself, as described in the Warhammer 40,000 Core Book, with the guidance detailed below.
All IMPERIAL KNIGHTS units (excluding FREEBLADE units) are drawn from one of the noble households. When you include a unit with the <NOBLE HOUSEHOLD> keyword in your army, you must then do one of the following:
Declare this unit belongs to a noble household, in which case you must nominate which noble household it is from. You then replace <NOBLE HOUSEHOLD> in every instance on its datasheet with the name of your chosen noble household. This could be one of the noble households detailed in a Warhammer 40,000 publication, or one of your own design.Declare this unit belongs to no noble household, in which case it is a FREEBLADE. You then replace <NOBLE HOUSEHOLD> in every instance on its datasheet with FREEBLADE.
Example: If you include a Knight Paladin in your army, and you decide it is from House Hawkshroud, its <NOBLE HOUSEHOLD> keyword becomes HOUSE HAWKSHROUD and its Paladins Duty ability reads ‘In your Command phase, you can select one friendly HOUSE HAWKSHROUD ARMIGER-CLASS model within 12" of this model. Until the start of your next Command phase, each time that ARMIGER-CLASS model makes an attack, re-roll a hit roll of 1 and re-roll a wound roll of 1’.
If your army is Battle-forged, you cannot include units drawn from two different noble household in the same Detachment, but it can include any number of FREEBLADES in the same Detachment.