Ingrid:
 
You're right: the announcement of how many recipients
are for the individual mail, not digest, index, nor
nomail.
 
Of course if you have redistribution lists or NETNEWS
gateways, you don't know how many are receiving.  And
of course if you don't do list maintenance viz "bounces"
then of course that further befuddles matters.
 
If the list has enabled the definition of STATS, that
too might prove of interest, as will searches of
the archives (if any) by date range i.e.,
 
S * IN listname FROM mm/yy TO mm/yy
 
/P