I really enjoy Curve as well, and I am absolutely blown away by how poorly Claiborne managed the marketing for this scent. How on earth did something that so easily fetches compliment after compliment end up in the bargain bin for $15?!
To answer your question: the reformulation came when Curve switched to EA Fragrances in 2009. I own a bottle from 2007 and a bottle from 2012. They smell pretty much identical. When I first realized they were made by different companies, I thought about seeking out a vintage bottle, but I tested them both and found very little difference, if any at all, so I decided not to bother.
Curve is easily my most complimented scent, followed by GphII, Aventus, Bvlgari Black and others, but honestly, Curve gets me more compliments from women than all others combined. That alone shows what a ridiculous bargain it is. The funny thing is, I HAVE NO IDEA WHY Curve gets so many compliments! I mean, yeah, it's a great scent and I really do enjoy it, but it certainly isn't louder than the other scents I wear, and it doesn't have a smell that I would consider to be sexy. I actually made a woman blush once because of Curve. We're friends with zero sexual chemistry... but one day, we were out doing some street photography and she turned beet red. I gave her a WTF look, as if to say "Are you ok?" She said "Whatever cologne you're wearing... it's... uhm... really really good." I just kept thinking "Curve? REALLY?" Another time... I was dating a woman who makes scents. The first time we ever got physical, she stopped and said "Oh thank god you smell good" and there was a weird pause because I could tell she wanted me to say what I was wearing but she didn't want to ask... and I certainly didn't want to admit it was just a frigging $15 bottle of Curve... so I did what any man would do. I kissed her. It's the ultimate way to change (and/or end) a conversation. Works. Every. Time.
Seriously. I have no idea what it is about Curve that makes it such a compliment catcher, but it really is.
Anyway... I just left myself a reminder to wear Curve tomorrow: old on the left arm, new on the right. Check back and I'll do a direct comparison between the two.