look. when you machine parts, there will always be a tolerance. meaning, each part, even if they are made by the same machine to the same specs will have some variance in the actual size. thats why you need many different colors (sizes) bearings to keep clearnaces consistent.
maybe your block has all green, maybe it had green, green, brown, yellow, green. maybe it has green, black, pink, blue, yellow. you never know, thats why you have to check.