Update error conditions

Spec.md

@@ -74,13 +74,17 @@ The platform client (PipelineClient) is currently configured to retry on failure
  - 502 malformed request (message will contain detail)
  - 503 no worker available (there is no worker - either generic or scoped - available to serve your request)
  - 504 request timed out while waiting for a worker to complete
+ - 505 Container version not yet deployed - the requested version of the container hasn't been registered as a deployment target
 
 ### Class II - Platform worker errors
 
 Unless there is a deployment in progress, it is unlikely that any of these codes will benefit from retry. Two possible exceptions are 512 (which might be due to a recoverable network glitch) and 511 if (and only if) the targeted version is known to have been recently released.
 
  - 510 generic worker error, ideally unused, but context will be provided in message and potentially in logging
- - 511 container_version unavailable - the requested language:version pair isn't deployed. It may be in future
+ - 511 container_version unavailable -
+     the requested language:version pair isn't deployed. Because this isn't a 505, the router thinks that
+     it should be deployed onto a worker, therefore it's reasonable to assume that it maybe in the future
+     and retry.
  - 512 failure in container setup (container not spawned, maybe we're out of disk or s3 transfer failed)
  - 513 failure in container invocation (container exited with non zero code)
  - 514 output missing (container exited with a zero exit - so successfully - but the expected output was not written)