Grab yourself a copy of Microorganisms in Foods and use the investigation sampling plans in there for future incidents. At minimum I would determine what risk a positive coliform count indicates, then move on from there.
Your sampling plan depends on your goals, as Charles pointed out, what your retests will show you largely depends on the nature of the contamination, very rarely is contamination even throughout the lot, and working with a quantitative microbial limit at those low levels is not usually meaningful.
Typically, when suppliers state limits of <10 or none detective, they're looking for qualitative testing (presence/absence) and don't care about the number. And in a baked product it should pretty much be zero.
Retesting the original sample while also testing additional stratified samples throughout the lot and around the timestamp of the original can help you out. If all came back negative including the original, it could potentially have been sample contamination. If any of the retested samples (including the original) come up positive then you're back in a hard place where you can't say that there wasn't uneven contamination.
Those pesky "<" signs do occasionally go missing however, double check with the lab.