Thanks. So: 1. Corrected code provided; 2. Abbreviation works OK; 3. "Who are the main users for this?" Me! You wrote my planned follow-up question ;-) . I'm working on a linked abbreviation (like your OCLC example is).
The situation: I applied some wikilink+<abbr> in: en:Template:Kennedy family tree/sandbox (this version), see e.g. abbr "Ftz-H" in row four. The abbr expands, and the link is an page-internal link, #anchored: [[#Ftz-H_parent|.. label code (=abbr tag) goes here...]].
The workings: The abbr-wikilink shows as expected (both underlines). Hovering the abbreviation expands nicely in a "tooltip". Clicking an abbr-wikilink makes the cursor jump nicely to the target anchor.
Complication/distraction in the example topic: anchors are mutually paired (the target location is an abbr-wikilink too. It jumps back to the original one. In the graph, it is to replace a too long connecting family line: parents-child).
The question: Combining wikilink and abbr is curious. Still, I think top level W3C design allows it by principle. Is there a reason to *discourage* its usage from this top level point of view?
A secondary question: is there a problem in this with hovercards? (I say secondary, because IMO hovercards can not dictate/overrule W3C guidelines). With me, they show OK with "tooltip" abbr in foreground.