Sure, and it's easy to tell the difference usually. Mouth, pussy, ass, they're just built different.
Now, an ass that's been well used, if you're wearing a condom, could probably be harder to tell from a warmed up pussy.
And yes, you can usually tell if a pussy has already been well fucked. The muscles tend to relax after the first few. If anyone ahead of you was allowed to come inside, it's definitely more slippery. You might not notice as much if you're wearing a condom, but if you pay attention you can tell the difference between semen and pussy juice even through a condom.
I rarely shared a woman with other men where I was willing to not use a condom, but you can absolutely tell the difference then, without question. I've been the first one in, and gone later in the train, and it is unmistakable, even without anyone coming inside.
With enough men, it may not be pleasant though. A lot of women will stop being able to lubricate on their own, and if they don't want artificial lube, it can get into the kind of pain that isn't fun trying to go at it the way is usually wanted in a situation like that. Most women I encountered that wanted a gang bang wanted it to be hard, forceful. A dry pussy hurts a bit to get into and can hurt a lot to fuck. Trying to fuck hard, and even with a love of pain, it can be too much.
So, if you're prone to running out of your own juices, plan ahead if you're taking more than two or three in a row. Have lube handy, or be prepared to be raw by the end of things.