Extra CSS Classes not applied to horizontal tab buttons li element

Hi guys, Subject line deliberately copied from another very similar which I though was covering the same issue. I believe this is a familiar issue - in that there doesn't seem to be a way of targeting a specific horizontal button/tab with additional css in the use case scenario, mine in this case, where we want to add icons to horizontal tabs AND where NOT all tabs will be displayed on every page - but haven't been able to find a solution/reply anywhere that covers it.

The use-case scenario is as follows (in case there is an existing technique/solution out there):

1. A luxury travel operator, in this case, has hotel content grouped into horizontal tabbed content items containing a Review, Feedback, Facilities and Videos.
2. Not every tabbed content group will have content. Some don't have Feedback and some don't have Videos.
3. Current li output typically contains class="horizontal-tab-button horizontal-tab-button-0" running sequentially regardless of actual content group. This is perfect where every tab group contains content (as subsequent tabs could be id'ed with button-1, button-2 etc for the additional css classes) but doesn't help when a content group is missing.
4. At first I assumed that either the customisable ID element (in the Manage Display configuration options) could be used for exactly this purpose (it can't, that updates the anchor ID instead) or the Extra CSS Classes (which only seems to to update the Fieldset classes) and so I can't see another way to do this.
5. The query is, whether it would easy enough to enable the additional class markup from either of these configuration options (the ID or Extra CSS Classes) to be applied to the tab button (li element) for the above use-case scenario?
6. I can't imagine how this could cause a problem for other use-case scenarios - but regrettably I'm not a back-end developer or I'd test this myself directly.

Do let me know if I can provide any further data/feedback to help - or if there is a way that the existing fields/display options can be arranged to generate the classes needed in the above scenario.

Many thanks,

Q.