"How should I edit your above-mentioned(1) comments without offending you?" wrote Jim to his sister, Jimina.
"Please don't edit anything, Jim", she retorted, "Just leave the abovementioned(2) alone, as usual. I'm far too agitated to hear your snarky criticism."
Jim bugged her, "The abovementioned(3) isn't really worth talking about, though."
She responded, "I'll have you know that my abovementioneds(4) do get read by and are respected by tens of people across this country, therefore they are worth talking about."
- singular or collective noun and verb conjugation
- plural noun (not collective) and verb conjugation
The highest probability is to find it in its adjectival form, hyphenated as in, above-mentioned.