I couldn't find any Wrigley Field threads. If there are, it was buried. I found this interesting photo from 1927. Apparenty the upper deck wasn't finished during the season and the caption said that only the 3rd baseline was double decked. But the vantage point from the photo looks to be taken at the upper deck level along the 1st base line. But you can clearly see along the left edge of the photo that the upper deck stops just before it turns behing home plate.