There were 47 Wilburs on set because the piglets grew up so fast. Also, each one was taught only one "trick", like to stare up or to walk a certain distance.
According to the 2007 DVD director's commentary, Templeton's feasting at the fair sequence was expanded after a test audience missed the Sherman Brothers' (Robert B. Sherman and Richard M. Sherman) song, "A Veritable Smorgasbord," they remembered from Charlotte's Web (1973).
When the two crows are discussing the scarecrow at the junkyard, one comments it has to be the same guy because he's wearing the same hat. The cutaway to the scarecrow shows no hat present.
Mrs. Zuckerman: I mean it was clear as day. T-E-R-R-I-F-I-C, I mean can you believe a spider wrote that? I didn't learn how to spell that word until I was in the 10th grade!
Wilbur: [looking at Charlotte's new web, at the fair]
But is is a good word, Charlotte? I mean, is it a TRUE word? I don't feel like I deserve all of the great words you've written about me...