CU 101 for my comrades:
Collateral underwriter is FNMA's appraisal underwriter. No human looks at it. When your appraisal is sent in, a CU report card comes back fastly, with a score.
The score goes 1-5 with anything 2.5, or below, lender is happy & safe. Above that means something not perfect, like rural or odd property, or bad value.
Your report card will, or will not, have a list of comments. If CU is unhappy about something you get dinged with a red check mark, and an explanation.
CU will say, most appraisers used a $50 adjustment, yours was low, etc, etc, It dings you when you go against the group. Dings lower your score.
CU knows everything about every property since the beast has been feed every appraisal for 50 years.
Now the underwriter gets your report card with the ding comments. They do not go into CU. They can waive any dings they want to. The big issue is your score.
The lender's staff reviewers can go directly into CU. CU has layers of information about whatever you are looking for. It does, however, suck at saying, look at these comps, which it will if unhappy about your comps. It seems to find comps in the same census tract, not necessarily da neighborhood.
With CU on your desktop, you have an advantage of pre correcting any CU unhappiness. So the AMC staff appraisers won't be given CU advice before the appraisal is sent to lender. And won't you get many AMC stips for CU dings, especially because the AMC don't care how stupid the ding is, or even understand them.