You've mis-read the documentation !!
| You can set the keep days of individual newsgroups. Run the command
|
| newgroup <name> <keepDays> [<maxDays>]
|
| where <name> is the newsgroup name and <keepDays> is the number of days
| that articles in the newsgroup will be kept before the expire program
| deletes them. The optional parameter <maxDays> is the absolute maximum
| number of days that articles containing an Expires: header will be kept.
What you've specified is that articles stored in the Yarn database
group alt.music.u2 expire after 4 (FOUR) days.
[If one of those articles has a line in its header saying that the
article's information should not be discarded until 12/31/96, what
your active file specifies is that even *THIS* article should be
expired by Yarn after 60 (SIXTY) days. (If the Expires: header had
instead said 7/4/96, Yarn would expire it on the header indicated
date, since that is sooner than the 60 days group default.) ]