It's hard to know for sure, as our school is quite opaque and close-mouthed when it comes to questioning the math curriculum; also, they don't really follow any one textbook but use a lot of district-designed materials, so it's hard for me to know where units would traditionally fit, etc. For example, DS's 7th grade math has already covered several algebra units, they also do a bit of geometry, graphing, etc. DDs geometry class just spent a while on some trigonometry, etc- as you noted, the common core units are aligned differently.
This is what my district is doing as well. The explanation I've been given is that there aren't any GOOD common core materials out there, and our district works on a 7 year cycle replacing text books and it's not time yet. So they are implementing common core by using a variety of materials they already own.
