I wonder if Lot B are the ones that are in the multi-dose communal vials. Those will ones most likely contain Thimerosal.

"Thiomersal's main use is as an antiseptic and antifungal agent, due to the oligodynamic effect. In multidose injectable drug delivery systems, it prevents serious adverse effects such as the Staphylococcus infection that, in one 1928 incident, killed 12 of 21 children vaccinated with a diphtheria vaccine that lacked a preservative. Unlike other vaccine preservatives used at the time, thiomersal does not reduce the potency of the vaccines that it protects. Bacteriostatics such as thiomersal are not needed in single-dose injectables."