Depending on how long you have been around, Dish has gone through different naming systems(why I don't know). Dish had the America's Top xxx packages in the past, changed the package names, to Bronze, Silver and Gold, and now Have changed them back to America's Top xxx Packages(Metal colors never did make much sense). Gold package is now America's Top 250.
You paid $10 for the HD versions of the SD channels in your package, and paid $10 more for Platinum which were channels that didn't have a SD counterpart. Last August, they combined them so if you had Gold, Silver and Bronze+(I believe on the Bronze level) you could get your HD level and Platinum channels for $10 instead of $10 each.
Platinum channels in the 361 and up to 394 currently, and you wont find the Platinum channels in the 9xxx area as, 361-394 are there original mappings.
94xx channels are the orignal mappings for the HD channels, but you can use a feature to map them down to their SD counterparts, or map them down and block out the SD counterpart so you only see 1 channel.
I personally map down, and then lock out the SD channel. ie, ESPN, channel 140 is mapped down from 9424, but instead of seeing a HD and a SD version of 140, I lock out the SD version of 140. Its easy to do as the HD is labled HD. I don't see a reason to learn a new channel number, when I am already used to it. I hardly ever use the 94xx channels at all, using the map downs also make it real easy to spot a new HD channel, as Dish doen't always announce new Channels, and when you see two channel 135's you know Dish has added new channels.