This is a bit confusing to me. If I have voice 1 complete and want to enter voice 2, I hit “v”. The caret note shows the stem flipped down with NO number and when I enter the note, it goes to voice 2.
On the other hand, if I hit “v” twice, it shows a “2” with the caret note stem flipped down and when I enter the note it goes to voice 2 as well.
AFAIK Dorico does not number the first additional voice. Use voice colors to verify this.
If you have entered a voice with stems up, and hit “v” nothing happens, so I assume you mean shift-v. D. then suggests to add a voice with stems down. If you press shift-v again it will first suggest another upstem voice (2 then means 2nd upstem voice), then another downstem voice, which may or may not be confusing, depending of what you have already entered. As Derrek suggests, switch on voice colors, and remember that just v cycles thru the voices you have already created. D. doesn’t think about voices as being numbered… 
So when it shows “2” it’s really “3” and “3” is really “4”. I think it’s a bug because it makes no sense. Also, there are people with color blindness, so using colors to verify voices may be dificult.
No, Nicholas, you have misunderstood the numbers. For number 1 (which does not show) you have the first voice stems up and the second voice, stems down. Then number 2 is for the next couple of voices (stems up and down) and so on. So when you see the number 3 with stems up, it actually is like voice 5 — but as fratveno has written, Dorico does not handle things this way 
Thanks for the clarification.