sh: wait-ing for an already terminated background job

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

In sh, is it defined that it works to wait for a background job that has 
already terminated the time wait is invoked? SUS talks about PIDs "known 
to the invoking shell" and I'm not sure if something else than wait-ing 
can make a PID unknown.

Is there a more elegant portable (i.e. not using wait -n) way to background 
several commands and collect their individual rcs than remembering their 
PIDs and which PID corresponds to which command, then looping through the 
PID list, wait for each one in turn and associate the rc with the command 
remembered? Is that defined to work?

In case someone is wondering: I want to scan (dd -of /dev/null) several 
discs in parallel and of course gather which one, if any, failed.