Articles inbound for a particular news group which is not carried at a server are rejected and simply fail to appear in the outbound feeds of that server. For this reason many large commercial usenet servers, such as HiWAAY's, maintain several 'crossfeeds' with multiple usenet servers, thus an article missing from one inbound feed may very well appear in another inbound feed from a different source. The crossfeeds help with outbound posts as well, because different outbound feeds will accept different sets of articles and forward them to different servers. Crossfeeds in non-commercial usenet news servers are rare because they consume enormous amounts of resource. Propagation delays also vary greatly over time, based upon general usenet traffic loads for a particular period.
Delays get worse when many posts nationwide are made and better when fewer posts nationwide occur.
Heavy traffic in the alt.binaries and alt.warez groups because of their size can clog usenet feeds for many hours, even days. This often occurs when someone heavily spams the newsgroups with a large binary or Microsoft releases a new version of some software product that the warez pirates repeatedly post to usenet as huge binaries. The bottom line is a typical propagation delay is on the order of a day for most of the usenet system, but posts from HiWAAY usually do much better than the national average. For public servers connected via major backbones, you can expect a propagation delay for most popular newsgroups of a few hours. For less popular newsgroups and most private servers not connected by the major backbones, the propagation delay from HiWAAY is usually about a day.