Here is Rabbi Rosen quoted in HaTzofe:
שניהם, בנפרד, גערו ברב דרוקמן שהבטיח לא לשנות באיוולת זו, ושניהם הורו שלא לערוך גיור מחודש ואפילו לא להחליף תעודות מחשש לחילול השם. כמובן שקבלתי בשמחה ואישרתי את כל גיורי הרב דרוקמן
Both of them [Rabbis Shapira zt"l and Eliyahu shli"ta] , in separate, castigated Rabbi Druckman who promised not to repeat this foolishness [of signing conversion certificates for conversions where he was not present] , and both of them instructed me not to perform a renewed conversion [i.e. the converts do not have to repeat the conversion ceremony] and even not to replace the certificates for the fear of desecrating God's holy name. As is understood I received [this instruction] happily and I certified all of Rabbi Druckman's conversions.
So here it is, black on white, that the former Chief Rabbis ruled that the conversions are just fine in spite of the "forgeries", and as Rabbi Rosen wrote:
With regards to the conversions that were already performed - since in the end there were three rabbis that sat in judgment, the conversion is valid because the certificate as a document is not necessary according to Jewish law, and even if there is 'a forgery in it' this does not harm the conversion. As is understood that such a decision intrinsically implies that he who signed [Rabbi Druckman] this kind of 'forgery', and also Rabbi Avior that caused [Rabbi Druckman] to sign because of a certain interest, and is himself [Rabbi Avior] a signatory as well, there is nothing in all this to cast a personal blemish or illegitimacy to judge [on Rabbi Druckman or Rabbi Avior].
Now I need to try to understand Rabbi Sherman shli"ta and his esteemed colleagues in the Great Rabbinical Court in Jerusalem. In their ruling they quote Rabbi Rosen at length, obviously accepted what he wrote as reliable. The head of the court, Rabbi Sherman wrote:
Among all of the voluminous material that exists in the file on the conduct of the Merkaz Shapira Conversion Court, and the conduct of the Court President Rabbi Druckman and his deputy Rabbi Y. Avior, I did not find any reaction, responsum or opinion by any expert rabbinic authority to the piercing halachic questions of Rabbi Yisrael Rosen, former head of the Conversion Administration.
Nu, because they found nothing in the file they decided to answer Rabbi Rosen's questions by themselves, arriving at conclusions that have serious implications for the converts. They mention that Rabbi Rosen sent questions concerning the matter to Rabbis Shapira zt"l and Eliyahu shli"ta. However, did they bother asking Rabbi Rosen if he received an answer from the Chief Rabbis? Although the answer received from the former Chief Rabbis was apparently oral, Rabbi Sherman obviously considers Rabbi Rosen's testimony reliable since he quoted him at length, as I have already mentioned!
At his point, as far as I am concerned, the instructions of two former Chief Rabbis outweigh the deliberations of Rabbi Sherman and his court. To be continued.