Edge retention is how long a blade stays sharp under given conditions over a period of use, as Boker's knife glossary defines it. Boker says the blade material, the production process used to make the blade and its edge geometry determine it, and names the behavior of the user as another major factor.
Boker's definition carries a condition: how long the blade remains sharp "under certain circumstances and over a certain period of time." The same edge dulls at a different rate on different material and in different hands.
The material is the alloy, in the Steel Lab; the production process takes in heat treatment (Buck says its own blades are tempered to the appropriate Rockwell hardness) and, for some steels, the powder metallurgy route. Which alloys last longest is answered in what steel holds an edge the longest.
CATRA says its Automatic Edge Tester conforms fully to the cutting test standard BS EN ISO 8442-5:2004. The blade cuts back and forth into test card loaded with 5% silica, which wears the edge mildly; cut depth measures sharpness, and depth over successive strokes is plotted as a wear curve.
ISO scopes ISO 8442-5:2004 to hand-use knives for "professional and domestic use in the preparation of food of all kinds", and says testing knives of any construction or blade material is not precluded when the test criteria are met.
Crucible's CPM 20CV data sheet (DS 01/16) reports a CATRA result relative to 440C and calls it "a relative measure of edge retention and wear resistance"; Crucible's S30V sheet calls the same test a measure of relative wear resistance.
Each Steel Lab entry has an edge retention line: a word rating with a note, such as Very good for S30V or Moderate for 14C28N, carried from the verified steel records, which draw on maker datasheets and independent references. It is not a CATRA figure and not a test Knives Now ran. Read it alongside the other factors Boker names: the production process, the edge geometry and the behavior of the user.