When was this netflix rule implemented?

I copied the following from NEtflix's site, after having a problem
with my account. I have always been able to watch with 2 at a time,
why the change/ when did this begin?

Q:
Can I watch movies instantly on more than one PC or Netflix-ready
device?

A:
Some membership plans allow you to watch simultaneously on more than
one personal computer or Netflix-ready device. If you are on the Watch
Instantly Unlimited plan or the 1-disc-out-at-a-time plan, you may
watch only one device at a time. If you are on the
2-discs-out-at-a-time plan, you may watch on up to two devices at a
time. Members on the 3-disc plan can watch on up to three devices. The
maximum is four devices --- available for members on the
4-or-greater-discs-out-at-a-time plan.
Your account can have up to six unique authorized devices activated
(and associated with it) at any given time, including personal
computers and Netflix-ready devices. For example, if you're on the
1-disc plan, you can have up to six devices associated with your
account, but you can only watch one of them at a time. If you're on
the 2-disc plan, you can have up to six devices activated but can only
watch two of them at the same time.