Credit bureaus collect data independently of each other–and they typically do not share it. In addition, your creditors and lenders might report data only to one or two of the credit bureaus. The end result is that Equifax, Experian, and TransUnion credit reports might all look different from each other.
Each credit bureau calculates your credit score with the data in its credit file. For example, Experian calculates your credit score with the data in your Experian credit report. So, if you have a collection account that appears on your TransUnion credit report, but not on your Experian credit report, then your TransUnion credit score might be lower.