The origin and functional differences between the Classical Chinese function words 於 and 於 have long been controversial. One of the problems in investigating their functional differences using transmitted texts is that how well a transmitted text preserves the distinction between the two. In studying The Ceremonies and Rites 『儀禮』, it is of great importance that there exists an excavated version of it included in the cache of wooden and a bamboo strips found at Wuwei in Gansu province in 1959, which presumably preserves the earlier shape of the text as it existed in the late Western Han period. In this paper, it is investigated that how well the distinctions between 於 and 於 were preserved in a transmitted text through the comparison between 『武威漢簡』 and 『儀禮注疏』 compiled by Ruan Yuan 阮元 in 1816. It is discussed that while the distinctions were, overall, well-preserved, especially when 於 carried out its unique functions (such as a locative verb, a comparartive marker, or used in a prepositional phrase appearing before the verb phrase), they were occasionally confused when they carried out a shared function, such as a recipient marker or a locative marker. Finally, it is stressed that, by comparing the excavated text and its transmitted counterpart, one can observe the formation and modification of a text, including additions, elisions, or errors of later redactors. Also, by comparing an excavated text and its transmitted counterpart, one can also reconstruct the proto-shape of a text.