A survey of the recordings in the Okada Collection, a collection of speeches from the Taisho era to the early Showa era (from the 1910s to 1940s), shows that the most popular pronunciation of the word baai (場合) was bayai, and not baai. This is in stark contrast to contemporary Japanese, where, if we follow the distribution of dictionary entries, statistics based on the corpora, and actual pronunciations employed in Diet meetings, the word is pronounced as baai by an overwhelming majority. This paper attempts to account for the difference through examining corpus data, historical documents, and dialectological survey results. The form bayai appears in Sharebon, a late Edo-period novelette, from multiple dialectal areas; further, the On-in Chosa Hokokusho, the first official nationwide dialectological survey by the government published in 1905, indicates that bayai was a rather common dialectal form used in a number of dialects across the country. This paper claims that speakers from the Okada Collection simply used their native dialectal forms. With the spread of Standard Japanese after World War II, bayai has come to be recognized as a dialectal form, and in fact, even as a vulgarism. Baai, in contrast, emerged as the standard form that is widely used in contemporary Japanese. Although further research is required to trace the word's exact development in the post-WWII era, this paper demonstrates the historical value of the Okada Collection for the study of the development of contemporary Japanese.