Books in a series are sometimes titled as volume 1, 2, 3 and so on. When adding release titles in such cases, oftentimes the cover will be stylized to only use a number, use roman numerals, have the word Volume, Vol., or even Novel before the index, and some covers will add a preceding 0 before the index, i.e. 01. Most of the audiobooks I’m dealing with are digital-only releases, and I usually use the publisher’s website for information. Typically, the title on the website always uses the format of Vol. or Volume constistently instead of following the stylized format on the cover. Sometimes the titles on the publishers’ websites omit subtitles for the volume, even though this is on the cover. This means there’s a conflict between what’s on the cover and what the publisher lists on their website. It’s also worth noting that the actual books you read with your eyes may have a cover stylized differently than the audiobook, but will almost always be referred to with the exact same title as the audiobook in publishers’ listings, perhaps with a disambiguation in parentheses.
So which one should I follow? I typically always include the subtitle if it’s shown for either source. I usually apply relevant style guidelines, too. For instance, series that end with punctuation may include a comma before the Vol. word like Series!, Vol. 1, and I omit the comma, i.e. Series! Vol. 1 according to the guidelines. Also, if the best source is the publisher’s listing, I wonder if I should always either write Volume out or always abbreviate it to Vol. for consistency, regardless of how it appears. When titling works, I usually follow the publisher’s listing.
This discussion is probably also relevant to naming conventions for naming editions and works in BookBrainz when books in a series follow similar naming conventions.
I strongly believe that audiobooks belong in BookBrainz, rather than MusicBrainz, but, as long as they are present in MB, I would follow the MB guidelines.
For releases of physical media, the Release Title will be sourced from the front cover. When a physical cover is not available, find the title at a reliable online source. For digital media, use the label’s page or other official source. Avoid using information from resellers.
Although that explicit instruction only appears on the classical guidelines, I think most people follow it for non-classical music as well. I know that I do. If I were adding/editing audiobook entries in MB, this is how I would interpret the guidelines: For a digital-only audiobook release, the publisher’s website is the preferred source. I would prioritize the cover art, if the publisher’s page has cover art (and especially if it has a subtitle that isn’t mentioned outside the cover art). If not, then whatever they list as the title, verbatim.
If the publisher source/website is more consistent than the covers (hard to say without seeing examples, but I assume that the covers have ‘artistic license’, but the publisher has a more canonical way that they ‘actually’ title the releases) then I would use the publisher source.
If there is something on the cover that you think should be included in the title, and isn’t in the publisher source, I wouldn’t feel too bad about putting it together in whatever way makes most sense to you. Sometimes provided metadata is just messy and inconsistent (urgh) and then we have to try make it work. If other editors disagree that is what the voting system is for, or they can add their own edits later.
I personally would standardise Volume/Vol. if it’s for one series/publisher, picking whichever appears most often. However, only applied to related releases, e.g. if Label A prefers ‘Volume’ and unrelated Label B prefers ‘Vol.’, I would leave them to their own preference.