How to select and query individual DCC servers?

I've been noticing _some_ inconsistencies in responses from DCC
servers for some time now.   I'd check the checksums on DCCed
mail later in the same day when a different public server was 
handling the request .. and recieve a count=0 for example.  I
didn't understand how the checksum flooding mechanism worked
well enough to ask about it.   Never enough time:(

When the news about the checksum flooding problem came out I thought
that was the reason, and I stopped thinking about it.

However, still, there are some servers that do not seem to have
checksums updated on them.   Others seem way behind the game.
This makes DCC less than useful if you are talking to those servers.

Two questions:

1) Is there a way to select an individual/list of DCC server(s) to
query, so I can compare the checksums on the various servers?

2) Is there any good way to not use particular dcc servers?  For
example ones with "good rankings" RTT-wise, but that hvae poor
checksum databases?   Currently I've installed blackhole routes to
those servers, but I was wondering if there was a good way to do
it with dcc.

Thanks for any info
Bolo -- Josef T. Burger