The transcripts of the closed hearings - not heard by the jury - were released by an appeals court in a case brought by media organisations.
They show Deputy District Attorney Ann Rundle arguing that Ryder had a history of shoplifting before the incident at the exclusive Beverly Hills Saks Fifth Avenue where she stole goods worth $5,500 (£3,500).
"We have videotapes of two prior instances wherein she is seen doing the identical conduct that they will see on the video in our case ... selecting items, concealing those items underneath heavy garment bags or underneath her own clothing, in and out of dressing rooms and ultimately walking out of the store without paying for the item," Ms Rundle said.
She said that in one case Ryder "was seen by security selecting a hat, wandering around the store and then walking out the door with the hat on her head without paying for it".
The alleged incidents took place at Barneys and Neiman Marcus stores in Beverly Hills in 2000 and 2001, but no charges were brought.
The two-time Oscar nominee is due to be sentenced on 6 December, but the prosecution have said they will not demand a jail sentence.
In another development, a court document which could help judges sentence the actress has disappeared, Los Angeles County officials said.
The document - containing information about Ryder's marital and financial status, medical history and criminal record - was kept in a locked cabinet of Los Angeles County Probation Department.
A spokesman said an investigation was under way into the "unusual" disappearance, but added that back-up copies did exist.
Grand scale
Ryder did not take the witness stand during the six-day trial, which heard how she cut security tags off clothes and bags before walking out of the store without paying for them.
The court heard that she went to the Saks Fifth Avenue store prepared for a shoplifting spree with scissors, a garment bag and tissue in which to wrap the stolen goods.
Prosecutors said the star paid for four items but stole another 20 under her own "bonus programme".
The defence said Ryder believed Saks would keep her account "open" while she shopped and charge her later - but there was no evidence of an account.
The verdict is a huge blow for one of Hollywood's hottest stars, who made her name in films like Little Women, The Age of Innocence, Edward Scissorhands and Girl, Interrupted.
The jury of six men and six women included several of Ryder's Hollywood peers - among them the former head of Sony Pictures, the studio that made three of her best-known films.