You think the '90s are hard to fit into a classic hits format? Wait till you try to do it with '10s music!
That’s interesting. I feel it will be opposite. A lot more music crossed format lines in the 2010s. Mainstream formats like CHR, Hot AC, and even AC shared more new music than ever in the past decade and a half. In the ‘90s and even early 2000s, you had a lot more “AC-only” songs (just as one example). That’s a rarity these days.
Format designations aside, I think the ‘90s are the anomaly decade-wise, but I guess time will tell!