iserith
Magic Wordsmith
For stuff like dragons, I'm generally using the CR of the young dragon of the particular type. And often the PC has advantage (if there's a check) because I tend to treat dragons as "storied," meaning there's a lot of lore out there about them. I mean it is Dungeons & Dragons after all.How do you handle dragons, or any creature with multiple CR versions? If you going against a ancient red (DC 32 lore check, I think) and don't succeed, but you are high enough to get information on a DC 25 lore check for an adult red, wouldn't that still get you some useful information?
I would add that this method of using CR to determine DC is really best if you're not planning on going past tier 2 (maybe early tier 3) for a given campaign. If I'm going to have a campaign that goes to 20th level and thus using a lot of higher CR monsters, then I'm winging the DCs based on rarity of the monster relative to player's reasonably specific description.
It should also be noted that even on a failure, I'm giving some information. It's just not what the player wanted.