Thanks for taking the time to look Tmar
I can't find any information that even confirms they had ANY ATB/MTB bikes in 1985
It seems like before 1986 the Diamondback brand was focused on BMX. I don't think they sold many mountain bikes before this time, as it's pretty rare to see the Ridge Runner / Mean Streak lugged mtbs or the other Sand Streak or Trail Streak models mentioned in the 1984 catalog
I'm beginning to suspect the Apex and Ascent lines were introduced for the 1986 model year. I think I actually own one of the earliest ones from that model year, as the SN indicates late 1985, and the tubing is Tange Infinity, which I haven't seen on any of the frames produced in 1986.
In the mountain bike magazines i've found online, the first advertising for Diamondback mtbs I've seen is for the 87 Arrival