Yes ComJam, but we do not have the capacity to co-ordinate against every single departure that does not check in before levelling off.
The system capacities (Target Sector Flows) are designed to tolerate unforseen circumstances, but clearly are not designed to tolerate every departure not checking in!
As a bit of "cockpit groupie" I am well aware of the high workloads immediately after departure, so by all means delay the initial call until a convenient moment in the clean up-schedule, just don't leave it too long!