Items with no availability shouldn't show up in suggestions
When a bib record has 0 available items (all items lost or missing), it shows up in the 'You May Also Like" section. When clicked on, it takes the user to a 404 page.
It seems that these items are suppressed in direct searches - so they should probably also be suppressed from being suggested.

There is no way to accomplish this type of restriction in the records that are sent to syndetics as a representation of the bibs that are available in the catalog.
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Michael Biggs commented
There's really no way to filter the bib records before they are sent to Syndetics? Or no way to filter the data coming back from Syndetics?
At the very least it would be nice to have a 'no available items' page instead of a 404. I guess I'll make a new suggestion for that.