i tried to add your servers and hltv and another random server from my 1.6 server list. the result is that pinging worked fine for all servers, look
here.
status information only worked for the HLTV though, the others were displayed as being down. so this is an issue and i added it and it will be the first thing to do when i continue to work on the plugin. i am sure it has nothing to do with your server being old.
i think i already know what the problem is:
i was remembering this wrong, i only tested pinging on 1.6 servers and not status information. so it probably never worked yet.
when i started to write the plugin i already knew that since steam HL1 got a different format for such information queries. but somewhere i read that they would continue to support the old system as well for backwards compatibility so i decided to only fit the plugin for the old system so that i won't have to code 2 systems but only 1.
now in the end it looks like the information about backward compatibility was just wrong. if this is the case expect an update soon - it will be easy to code.
when you say ping checks didn't work: please note that within first QUERY_INTERVAL seconds (60 by default) after server (re)start the server is not checked. so when you restart the server and immediately connect to it you will see them all displayed as being down until 60 seconds went by. please be aware of that when testing and try it again with redirect_check_method 1.