Turns out there's quite a bit of writing about apprenticeship agreements, whether such contracts were enforceable, the "decline" of such agreements, etc. Here are two articles; their data set centers on Montreal, not Pennsylvania or even early America, but the articles are helpful anyway in that they are recent & summarize what others have written on these topics. If interested, read away!
"Enforcement in Apprenticeship Contracts"
https://www.dropbox.com/s/qopk8zb72meu6m2/Decline.pdf?dl=0"The Decline of Apprenticeship in North America"
https://www.dropbox.com/s/qwndcx8yes11bqq/Enforcement.pdf?dl=0FWIW, here's the apprenticeship agreements from 1805 that bound Matthew Henry (1790-1862) to a Lititz shopkeeper--so, this agreement occurred within the Moravian church. But, as late as 1805, such agreements were still ordinary practice.
I also found, after much searching, photos I took in 2017 of the "template" for apprenticeship agreements that the Moravians used. They're worth reading. One of the articles above notes that "In the United States and English Canada, very few early apprenticeship contracts still exist"--but
many such contracts survive in Moravian archives. I wonder what studying those would show?