Who's 18month old dog are you referring too? and if it's mine who evaluated it at SH????Hmm go run them both and see what happens; Main difference is running against other dogs vs. running against a standard. As for needing an HRCH or MH before running a FT, Whelp apples and oranges; It's all about skill set, not titles; a derby dog needs to be able to mark (singles Doubles, I've not see a triple but who knows). A qual dog needs to be able to mark (doubles triples, quad who knows) and run blinds (which are their own separate series). Theoretically best dog there that day takes the prize. The thing about FT is until you try them you just don't know. Varying degrees of difficulty is seen in both venues, but usually you don't need a completely finished MH to run a qual.
Ex; Our group decided to run a couple of Quals this year (peer-pressure ), 3 dogs are Finished MH-HRCH, (we don't train for FTs, their titled out) they play well, usually in till the end, 1 dog is an SH (transition) level ( also in till the end). Another friend has a 18mt still in derby/SH level (transition work)(her first qual she saw every series).
on the other hand; I know a few people that have young QAA dogs, they are also in (transition) some run Master-some aren't ready for it yet. Overall the dogs are in need of a bit of seasoning/ they aren't ready to consistently pass every test; but most of the time they play.
Now if your thinking of wrangling the bull and throwing your hat into Amateur-Open you need a FINISHED and experienced Dog. Figure those that play the FT game and only the FT game every day oftentimes don't see every series. So you need a finished dog, with FT experience and need to be pretty finished and experienced yourself; a bit of luck never hurt .
I've contemplated throwing my dog into an upper stake, as I did the Qual (just to see); however I'll just never be as into it nor as dedicated as most of those playing that game. I'll never put in the focused training-time required to play well and consistently, if I'm not going to play well and consistently; I don't really see the point. Doesn't mean I won't be conned into trying it