During the first grammarian's time, west norse dialects used 23
runes, as is well attested in extant inscription. They were:

fuþorkhniastbmly - the original 16 named runes
oøgeædp - 7 additional, based on the named ones.

o was originally hooked-o, but was inverted to form o in Norwegian
use about 1000-1030. Subsequently, the top bar was drawn through the
line to form hooked-o, leaving the bottom short (Junicode has it).
If both bars were drawn through the line, it was ø instead of o. k
and i were punctuated to form g and e, respectively. As the west
norse a-rune had its bar only to the left of the stave, it was drawn
through to form æ (just like with hooked o and ø). t was punctuated
to form d, and the top and bottom of the b-rune were drawn out to
form p (it looks like a mirrored k-rune). Simple enough. Now, this
is all that is needed to write Norse. Therefore, I commented that
the 1st grammarians claim that 'runar uisa oskyrt' is false,
countering that the common folk had already developed all of the
characters needed to write Norse before the 1st developed the new
Latin characters needed to write Norse with Latin characters. To
compete with the 1st, all that the common man would have to do it
add accents to lengthen vowels (or consonants - compare the 1st's
use of capitals to denote double consonants). And that's all. It was
really that simple in his time, which is what makes his comment here
unexplainable. He could just as well have added accents to his own
countrymen's runes (and dots if he wanted to denote nasals, but it's
never needed with short nasal vowels, as they always occur before or
after preserved n/m). Instead, the common alfphabet seems to have
been neglected, the cost being hundreds of years of illiteracy.
Writing, it seems, had to belong to the clerical elite, and the man
on the farm should not be able to read the elite's runes. It seems
that the Latin alphabet was a symbol of power, of association with
the current Holy Roman Empire. The problem was that the common folk
already had a sufficient alphabet by the 1st's time, having formed
it themselves from the original 16 apopted from Danish use about 300
years earlier. It's a fact of history that is conveniently ignored
by those who which to credit the church with the introduction of all
writing. What the church introduced was the art of making skinbooks,
which in itself has local and practical, rather than specifically
clerical, origins in Europe. Given that we cannot change history, I
will bet that our knowledge of history, and well as the number and
quality of ancient writings, would be far greater if parts of the
old tithe (the tenth collected by the church in taxes) were required
by law to go to the production and distribution of writing material
for the common man, with no alphabet-strings attached. Had that
happened in Iceland, then modern Icelanders would almost certainly
have their original alphabet to this day, given only that the forces
of the reformation had not destroyed it (possible), not to mention
that surviving literature would have a different character entirely,
with more diverging points of view, styles, contents, etc. This is
probably the only scenario in which one might expect something like
a full Eddic corpus with variants from local tradition to survive,
simply because it's what the common folk had to write, besides their
geneologies, family history, etc.. Sour food for thought, given what
happened. Still, the common folk still deserve full credit to this
day for their ingenious (and complete) native alphabet.