The formula was indeed changed, but has been improved/corrected.
I use Ceramcoat Brown Iron Oxide as my "basic" brown. When I bought a few new bottles last year, I found they were slightly lighter and certainly did not cover as well.
I contacted Ceramcoat and was told there a formula change had affected some colors but that it was corrected. They even sent 2 bottles of the revised formula free. Although improved, I can't say the new stuff matched the old stuff, but it is indeed better than the changed formula.
Also I was told the new improved formula has a cap seal that says "Made in USA" and the main label has a Lot Number. So look for that now when buying Ceramcoat.
Also -- the paint color names no longer state whether they're opaque, semi-opaque or transparent, so buyer beware. Ceramcoat used to have detail about this on their website, but the last I checked (months ago), that info was gone.
Good luck!