Serial Number and VIN (Vehicle Identification Number) are the same thing. The original Motor Vehicle Title that was surrendered to the Motor Vehicle Department when the Affidavit of Affixture was recorded, has it identified as a VIN, that is why it is reported that way on the Affidavit. They should be very similar on both documents, might be slightly different arrangement but the same digits. For example a recent report of mine had 157-OOP.H-006156A and B on the Affidavit of Affixture. The number on the Data Plate was 15706156 A / B OOP.H Slightly different but basically the same thing.
Now if you have numbers that are completely different--then there is a problem that needs to be straitened out by the owner's title company. So if that is the case, call the lender, tell them the problem and they need to go to work and figure out what the solution will be. If they want the report complete, then subject to the correction of title.
I did two appraisals about six months apart in the Duncan area several years ago. Both manufactured homes had originally been owned by the school district and used as class rooms. Then the district sold them to two different people. The Affidavit of Affixtures did not match the Data Plates. So the county assessor's office, an inspector from the motor vehicle department, two title companies and the home owners crawled under the homes to find out what serial numbers were on the frame. They finally figured out what had happened. When the district signed over the title to each owner, they just grabbed two titles out of the file cabinet and handed them to the new owner without verifying the information. Turned out one owner got both halves of home #A and one title for A and one title for B, that was how the Affidavits of Affixture were prepared. The other owner got one title for B and one title for A and their Affidavit didn't match. So they had to get the titles back from MVD, then the right titles were given to the right owners and new Affidavits of Affixtures recorded.
On the 1004C I type the serial number (VIN) from the Affidavit of Affixture on page one, on one of my photo pages I have a photo of the Data Plate and underneath type the serial number that appears on the Data Plate.