The form is confusing. First they say to use properties that compete with the subject, but then they call them comparables and say that the numbers on the MC form should match on page 2. But competing properties may not be comparable properties. I may be appraising a two story, but a ranch or split level could be a competing property but not a comparable property. Most buyers start their search by 1. location and 2. price. After that they may say I prefer a ranch, but look at a 2 story and decide they like it. They may start out saying I have to have new house but end up liking a resale. My point is that competitive properties will include homes that are not necessarily comparable properties. And by using competing properties it will likely give you a sample large enough to show a trend. I usually make a statement explaining the difference between competing and comparable properties and that the number may not match up with page 2.
And the trend shown on the MC could be different than the trend shown for the entire neighborhood on page 1. If your appraising a high end home it may still be declining but the moderate priced homes may be stable or increasing.