apt and package versioning

[Colin Law]

I am trying to understand an apt issue to with package versioning.
The issue has arisen on Raspbian Buster, but I hope there will not be
major objections to me asking about it here as the question is not
specifically about Raspbian.  The issue is that if I check to see what
version of npm is available for installation I see

$ apt policy npm
npm:
  Installed: (none)
  Candidate: 5.8.0+ds6-4
  Version table:
     5.8.0+ds6-4 500
        500 http://raspbian.raspberrypi.org/raspbian buster/main armhf Packages


But if I try to install nodered I get

The following packages have unmet dependencies:
 nodered : Depends: npm (>= 5.8)

I had assumed that apt would consider npm 5.8.0+ds6-4 to be >= 5.8, or
am I misinterpreting what the problem is?

Colin