I think that early-90s mustang saved it. Total game-changer.
Looking at the year-by-year sales, yeah, the Fox-body was down to 79K, by far the lowest figure ever. That doubled in 2 years with the early-90s design. That fizzled in the early-2000s, and the next design change bumped it back up in 2005. And another big bump in 2015.
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I was born in '80, and so all I knew growing up was the mid-60s (classics), and Foxbody before the '93/94 version came out. Those early-mid 70s weren't even a blip on the radar, which you explained why, lol. But my mind couldn't wrap around going from the 60s design to the Foxbody.....I didn't see the convoluted evolution, just the stark contrast of awesome to awful.
The 93/94 was a huge step in the right direction, and the further redesign in 05 was great, too.