About false reporting of how many msgs are in a group

[Harry Putnam]

I'm sure you all see this from time to time.

Some group you read often shows 3 new messages

You press <enter> from group buffer to have a look.

You are then prompted for how many messages you want see with the
default something like 237 (just an example)

But wait, it only showed 3 new messages but this prompt is saying
there are 237 new messages.

In fact there are only 3 but due to certain conditions gnus `thinks'
there are 237.

If gnus `thinks' there are less than 200 (I think might be the default)
then you are not even prompted as above.  

I'd like to have the latter happen when the correct number of new
messages is below the default.  Simply because its one less click and
tiny bit faster.

Anyone know how to reset things so gnus sees the correct number of new
msgs?

I remember reading long ago as to why that count becomes inaccurate
over time and with use, but I've long ago forgotten the reason.

But anyway isn't there (with gnus closed) 1 or maybe several text
files one could edit so that the message count is back to accurate for
a while anyway?

In the case of nntp groups, some tricky maneuver involving process
marking in order and moving to a tmp group then back is not an options
so how can we reset the count in the case of nntp groups?