אֲשֶׁר and שֶׁ־ are not identical across every register

אֲשֶׁר is a major Biblical Hebrew relative connector: it links a noun or statement to information describing it. The shorter שֶׁ־ becomes especially important in later Hebrew and also appears in biblical material, but the distribution is not identical across periods and genres. The curriculum therefore teaches the forms with their corpus labels instead of pretending one can be substituted for the other everywhere.