Volume numbers. Are mini series considered?

I've traditionally considered any Titles with the same as separate volumes. For example, the original wolverine mini series is Wolverine, Vol. 1 and the subsequent ongoing series stating in 1988 as volume 2. I prefer this method since Titles sort cleaner and are easy to find. Since I've been using comicvine I've found this isn't the case and mini series sometimes aren't designated as volumes. But sometimes they are. Is there a styleguide to volume numbering I missed?

Comicvine doesn't sort volume information in terms of 1, 2, etc. but in terms of year published. so V1989, V1990, etc.