In the Kaz Algar Summary / Faction Summary page, add some indicator (on toggle/hover or by default) to show you total crest potential based on exchange. I'm bad at math and this could help know my actual crest potential.

Meaning, if I have 90 Weathered Crests and 30 Carved Crests and 0 of all other crests,
I could exchange 45 Weathered x2 to the Exchange vendor. I could then have enough for x1 Carved Exchange to get some Runed.
So my "potential" Crests when I have 90 Weather, 30 Carved is really 60 Carved or even 15 Runed.