Well jls, here's the deal.
As the systems developed, and designs were changed, some power supplies were changed, it came to pass that some would power up slower than others.
Thus, when power was restored, if you had a slow one on the RIGHT and a FAST ONE on the left, then the right most carrier may not have been recognized.
Yes, that should NOT have been the result, but it was.
As far as whether you are powering down correctly or not, bottom line, powering down made no diff, but to help all parties concerned on the same page, we used to try to teach only one method. Again, in reality, the system cares not how it is powered down.