What does "a pattern not alway set in and grow" mean?

[on the way]

The following is a sentence I came across in my reading. “The eighteenth century, for example, produced from various sources a tendency to fix the language into patterns not always set in and grew.”
What baffles me is the expression “not always set in and grew” at the end of the sentence. My acquaintance of English grammar would immediately tell me that this part of the sentence should be past participles functioning as postpositive attributive, but I am puzzled by the awareness that “grew” instead of “grown” is used there, and, moreover, the meaning of “set in” as I know it makes the phrase, at least to me, out of place here. So here I am again, dying for help. Any reply will be much appreciated. Thank you all.

[5jj]

'... patterns set in and grew' is meaningless. There is some printing error here.