Things like "ponytails" and earrings are just a few examples of non-period things I have seen at recent reenactments. Sometimes people wear Early-war uniforms in a Late-war reenactment and vice-versa. While the former could happen, it's highly unlikely that a uniform would last that long as soldiers wore them every day until they were worn out and were issued new ones. The latter is totally inexcusable because most of the later war uniforms just didn't exist during the early war era. Most reenactors do some research, but some just buy whatever they find that suits their fancy. I hate to say it, but Confederate reenactors are probably the worst at wearing "farby" uniforms. Farby means unrealistic and unperiod, in case you don't know that term.
There are different levels of reenactors, from mainstream to hardcore. Mainstreamers tend to buy whatever looks cool or what they think is correct. Hardcores are the kind that are critical about everything and are sometimes called "stitch nazis" lol My unit is somewhere in between and what is generally known as progressive. People who are always looking to better their impression, but at the same time realize that the better museum quality reproductions are cost prohibitive for most reenactors.
You really don't have to worry too much unless you're doing scenes of specific battles, then you will want to do some research. And of course avoid guys with "ponytails", earrings and/or modern jewlery.
In any case, feel free to contact me if you have any questions or doubts about anything. While I'm not an expert by any means, I do know the basics and have access to a nice library of reference books on Civil War items.
1st Florida, Company D, Walton Guards