I don't know about "always", an embryo or zygote isn't "backwards", but at some point you can't tell me that a calf has enough room to flip around in there, actually would have to flip and turn or some how spin.  I'd say they are backwards for quite a while, definitely not a thing that just happens on day 269.

We had a cow that had a backwards calf two years in a row (one unassisted), I found that more interesting then anything.  Had normal last year and looks to be open this year.