Quick answer
Why do so many values here say Unknown?
Built from index records dated 2026-10-13 Compiled by an automated pipeline, checked by The Peptide Observer editorial desk How this site works
Because no record retrieved for that entry carried the value.
A little more
The alternative would be to fill the gap with an estimate or with a figure copied from somewhere unattributed, and this site does not do that. Every Unknown also carries a short note saying why it is empty, which is usually that a particular database was never queried.