The 3550 belt should decode that it is # 3 wide ( now 5/8 or 1/2 inch wide on top?) ( measure the old one) and 55.0 inches long measured on the front of the belt. the back of any belt catalog should match a belt. I always go to the “green stripe” section as they do not have the cogs. I will look at my Dayco book this morning and get back if you still need numbers.
The wrong belts you got would de-code to Tractor size 22 wide, 53.4 inches long which is why they are short by 1 1/2 inches.. in that catalog you would need a TR22550 if they make one or within a 1/4 inch of it. TR22553, TR22548 etc.