diff --git a/docs/missing.md b/docs/missing.md
index 7a5066d..a35acbd 100644
--- a/docs/missing.md
+++ b/docs/missing.md
@@ -15,16 +15,9 @@ specific files (patches welcome).
 * PREALLOC extents and extents containing blocks filled with zeros will
 be replaced by holes.  There is no way to turn this off.
 
-* Consecutive runs of duplicate blocks that are less than 12K in length
-can take 30% of the processing time while saving only 3% of the disk
-space.  There should be an option to just not bother with those, but it's
-complicated by the btrfs requirement to always dedupe complete extents.
-
-* There is a lot of duplicate reading of blocks in snapshots.  bees will
-scan all snapshots at close to the same time to try to get better
-performance by caching, but really fixing this requires rewriting the
-crawler to scan the btrfs extent tree directly instead of the subvol
-FS trees.
+* The fundamental unit of deduplication is the extent _reference_, when
+it should be the _extent_ itself.  This is an architectural limitation
+that results in excess reads of extent data, even in the Extent scan mode.
 
 * Block reads are currently more allocation- and CPU-intensive than they
 should be, especially for filesystems on SSD where the IO overhead is
@@ -33,8 +26,9 @@ much smaller.  This is a problem for CPU-power-constrained environments
 
 * bees can currently fragment extents when required to remove duplicate
 blocks, but has no defragmentation capability yet.  When possible, bees
-will attempt to work with existing extent boundaries, but it will not
-aggregate blocks together from multiple extents to create larger ones.
+will attempt to work with existing extent boundaries and choose the
+largest fragments available, but it will not aggregate blocks together
+from multiple extents to create larger ones.
 
 * When bees fragments an extent, the copied data is compressed.  There
 is currently no way (other than by modifying the source) to select a