It was sent in January this year, but it went to more people than it should have, cancelling care for people who still needed it.
Under the Official Information Act, RNZ received an internal DHB review of what went wrong.
The review said DHB staff tried to speak up about the decision but felt unheard.
Others wanted to say something but did not feel it was their role or place.
It said isolated conversations between teams meant there was no clear objective.
Jacky Braid said her 89-year-old mother thought she had lost her home care service for good when she got the DHB's letter.
"She was kind of quite shocked and gave it to me and said, what's going on here," Braid said.
"It was quite a surprise, it came out of nowhere."
After reading the review, Baird said "clearly there were major errors".
"It does concern me when you have staff at any level who feel that they can't speak to a manager about the processes that they're going through."
The National Party's MP for Tukituki, Lawrence Yule, also received the review under the OIA.
He said it showed why the distribution went "spectacularly wrong".
"It appears that nobody was really in charge of sending out a letter to all these vulnerable people to reduce the level of service they're receiving. And that's the biggest issue in all of this I can't quite comprehend that."
Public Service Association assistant national secretary Melissa Woolley said it was disappointing the review did not include the views of home care workers.
"Our members would have said that this was a bad idea right from the outset and they want to make sure that care is being delivered to the people they support in an ongoing way," Woolley said.
"They are the eyes and ears of the people providing these services and yet again, workers are missed out of a review."
She said the DHB's lack of communication with its staff is a wider health-sector problem.
The review recommended changes to ensure the mistake did not happen again, including encouraging staff to comment on management decisions.
The DHB refused an RNZ request for correspondence between its acting chief executive Craig Climo and the board regarding the problem, citing an employment matter.
- RNZ