With message IDs, it's relatively simple & quick to check whether the article is available on the server without needing to grab the whole header or start downloading the body - a single header field can be checked per message ID using the XHDR command, for example. This data is usually free, too.
So it would be helpful to have the option of manually connecting and *only* checking server completion of all articles in an NZB/node before doing anything else, and updating the queue with the info. If it can work smoothly, it might also be nice to toggle an automated check before downloading bodies, so we can get an early heads-up of any problems, and perhaps set some auto actions (such as autopause NZB if completion < threshold% and not enough pars to repair).