Random searches?

The Pasuk says "וַיְחַפֵּשׂ בַּגָּדוֹל הֵחֵל וּבַקָּטֹן כִּלָּה וַיִּמָּצֵא הַגָּבִיעַ בְּאַמְתַּחַת בִּנְיָמִן - "He searched; he started with the eldest and finished with the youngest, and the goblet was found in Benjamin's sack" (44:12). You would think this means he searched from Reuven's bag until Binyamin's bag. Not so. The Midrash Rabba says that the eldest referred to was in fact Shimon. And Yosef only searched this eldest and the youngest, Binyamin. The Griz, the Brisker Rav asks how the Midrash reached this conclusion.

He answers in the name of the Maharil Diskin that in 44:8 the brothers said a kal v'chomer, one of ten in the Torah, that" הֵן כֶּסֶף אֲשֶׁר מָצָאנוּ בְּפִי אַמְתְּחֹתֵינוּ הֱשִׁיבֹנוּ אֵלֶיךָ מֵאֶרֶץ כְּנָעַן וְאֵיךְ נִגְנֹב מִבֵּית אֲדֹנֶיךָ כֶּסֶף אוֹ זָהָב: - Behold, the money we found in the mouth of our sacks we returned to you from the land of Canaan; so how could we steal from your master's house silver or gold?". However, there are two people who did not make this kal v'chomer: Shimon and Binyamin! Binyamin was not there so he could not say he was as honest as his brothers who returned Yosef's gold, and in 44:24 it says " וַיִּקַּח מֵאִתָּם אֶת שִׁמְעוֹן וַיֶּאֱסֹר אֹתוֹ לְעֵינֵיהֶם - and he took Simeon from among them and imprisoned him before their eyes".

So the pasuk is actually telling us that the only people who were searched were the oldest and youngest of the people whose honesty had not been proven, Binyamin and Shimon!