There are a bunch of different FICO variants / scoring models / formulas, for example EX 04 vs. EX 08.
Because of this, scores will often not match, even with identical report data.
There are also time lag issues, for example if a week elapses between two score calculations, and the report changes in the meantime.
Lenders often use proprietary scoring systems, or FICO variants that don't match generally available scores such as the ones found here.
