Make sure it is in every rent appraisal you do whether attached to a 1004, or not.
You have a short history on this forum but that history is very consistent with wrong terminology and misunderstandings of Appraisal 101.
Spent my whole life judged, and discriminated against as a woman. Nothing new to me.
<Sigh>. There is no reason to pull out the "gender card" here. There are many on here who use screen names that do not identify them as male or female. I participated in a local forum for a coupe years using my dog's name as my screen name. My dog was a female, I am not. There are plenty of very intelligent female appraisers who don't need to pull out the "gender card" to get respect, they have already earned their respect.
Make sure you have a rent SOW too. Even in a 1004/GPRES a rent appraisal is a sub-appraisal.
You have cited the Dictionary of Real Estate Appraisal, 4th Edition for the definition of Market Rent and then you advise us (the forum) to put have a "rent SOW" and have advised that we need to include this definition in a "rent appraisal" and have also used the term "sub-appraisal".
Sitting behind me about six feet is the Dictionary of Real Estate Appraisal, 6th Edition and I don't need to pull that out or the Dictionary of Real Estate Appraisal 4th Edition (which you cited) that is buried somewhere in my office to tell you that you will not find the term RENT APPRAISAL or the term SUB-APPRAISAL in either of those books.
Somewhere, in some post on this forum, I think you talked about being a review appraiser. I can assure you that if you used some of the terminology in your reviews or used some of the wild ideas in your posts in a review of my work I would not hesitate to send it (your review) to the state.
Here is where you are VERY CONFUSED. Appraisal Practice is very wide and varied and includes things you most likely have never heard of as it appears your experience is limited to mostly lender form work (nothing wrong with that). HOWEVER, one would most likely use the definition you cited above for an appraisal of Market Rent which is not something that is uncommon.
Remember an appraisal is defined as an opinion of value. There are clients such as the federal government, state governments, private businesses and more that want to know what the Market Rent is in a specific area and the opinion of Market Rent is an appraisal. I have completed many of these as have many other appraisers. There are about 80,000 appraisers in this country and only about 60,000 have been identified as doing work for GSEs (Fannie, Freddie, FHA, USDA) work leaving about 25% (20,000) who don't do any GSE work.
Before you try to give advice to the masses you might want to consider your very limited experience and at least try to use the correct terminology in your posts.