That was the case about a year ago when I looked in to it.
We were in an audit at the last place and our service agreements stated that it only lasted the span of the current ndis plan, lots hadn't been updated.
Which itself was kind of stupid because when you sign people up, it's never on the same day the plan starts, people don't usually get them in the mail until about a fortnight after it starts.
So to make that system look right to the auditors you had to put in arbitrary dates in, the date you are getting it signed and the date the plan ended.
This is sort of because the auditors can only audit your made up internal systems, there isn't any standardisation.
This system didn't work for existing clients either because they'd be in the lifespan of the service agreement but then their plan would run out, then according to the service agreement, we couldn't provide supports inbetween the end of the current plan and the next one, there's usually a gap.
Which depends on when they have their reviews.
The system this place has is better, we don't have an end date for our service agreement, it's becoming best practice (I don't think any one does it apart from a few case managers) to go out when they have a new plan and sign a new service agreements.
But there's no legal reasons to, every company has their own policies and most don't even stick to them, or sometimes even know what they are.
Our system doesn't work either as there's a serious chance of exploitation.
Some companies charge for all interactions, so if the service agreement lasts forever, you could call up every month or whatever, then charge for the minimum time the service agreement charges for that service agreement states, which has no rules either.
I know that CARAs minimum time allotment is 3 hours, for shifts, not interactions, but if a service agreement said that, you could.
So, I could call basically an ex client and charge over $180 for him to tell me to fuck off, if I had a service agreement that said I could.
There are no rules, you'd probably get reported eventually or a rep or lac would cease the agreement for them.
About a year ago, you didn't need one.