The Pennsylvania Supreme Court has held that the unprecedented substitution of six grand jurors one year after the original panel had been sworn and begun its work was prejudicial to the defendant and necessitated the invalidation of the investigating grand jury's presentment and the subsequent indictment based on that presentment.
Commonwealth v. Levinson, 389 A.2d 1062 (Pa. 1978).
Richard J. Schubert,
Grand Jury - Irregularities in Function - Substitution of Grand Jurors,
Duq. L. Rev.
Available at: https://dsc.duq.edu/dlr/vol17/iss3/18