This article records tradition as it has been passed down and reported. Its sources are not yet part of the atlas's verified catalogue.
R. I. Page's introduction to English runes traces the documented process by which the older, twenty four character Elder Futhark was expanded in Frisia and Anglo-Saxon England to accommodate sound changes the older row could no longer represent, eventually reaching around thirty three characters in its fullest attested English form.
That documented expansion matters for a futhorc rune entry because it means the row a given rune belongs to is itself a real historical fact worth recording, an earlier rune inherited from the Elder Futhark reads differently in its documented history than a later rune added specifically to represent an English sound change, and an entry records that distinction rather than treating every futhorc character as equally ancient.
A futhorc rune entry therefore records where in this documented expansion a given rune sits, an inherited character or a later English addition, since Page's own account shows the row grew in traceable stages rather than appearing complete at once. Where a rune's addition is dated only approximately by surviving inscriptions, an entry says so rather than assigning it a false precise date.
The same entry records, where it is known, roughly how many of the row's characters were already present in the row's earliest attested English form and how many were later local additions, since that count is itself part of what makes the futhorc a documented, developing alphabet rather than a fixed set handed down unchanged from the continental runic tradition.