You (MSB) used propensity-matching to demonstrate the...

You (MSB) used propensity-matching to demonstrate the remestemcel-L survival benefit in high-risk patients based on Baseline MAP scores.
https://investorsmedia.mesoblast.com/static-files/cc68683d-f5c5-4dc0-b718-499c11fd8ca8

Regarding confounding factors - sure, but MSB is trying to demonstrate that the product works independent of the donor that provided the bone marrow aspirate. How can you do that if a patient gets MSCs from potentially 2 (or more) different donors, especially since MSB have shown different levels that could have affect clinical outcome (INFgamma - see Aggarwal & Pittenger: https://pubmed.ncbi.nlm.nih.gov/15494428/). Unless you say that is such confounding factor that can be found in any study. If that is in fact the case, then we may have a big problem.
MSB realised that this could be an issue (frankly, one that could have been avoided) after being prompted by the FDA and that's how you ended up with 11 data points (single lots in a single patient).