The cache includes lithographs, portraits, a watercolour and sketches created between 1900 and 1932.
Pierre and Danielle Le Guennec say they were given the art, worth 80m euro (£50m) by Picasso's second wife.
The Picasso estate says their account is "ridiculous" and is suing them for illegal possession of the works
Picasso's son Claude has insisted his father would "never" have given such a large quantity of works to anyone.
He told the French daily newspaper Liberation: "That doesn't stand up. These works were part of his life."
Prison sentence Le Guennec began working as a general handyman at Picasso's estate in the South of France in 1970.
He says that he and his wife Danielle were given 180 lithographs, collages and paintings and 91 drawings in 1970 by the artist's then-wife, Jacqueline. He claims she gave him the works in a closed box containing the works, saying: "Here, it's for you. Take it home".
Danielle recalled that her husband came home with a stuffed bag, and told her that Picasso had given the works to him.
The works, which have never been displayed publicly, were kept virtually untouched in Le Guennecs' garage until the couple decided to put their affairs in order for their children in 2010.
According to Le Guennec's lawyer, he started worrying around five years ago about what might happen to the works after his death.
He contacted the Picasso administration, which looks after works held by his heirs.
In September 2010, Le Guennec travelled to Paris to have the works assessed by the administration.
But within days of art experts proving the works were genuine, police swooped on the elderly pair at their home in Mouans Sartoux, near Cannes, and arrested them on suspicion of receiving stolen goods.
The seized Picassos include a watercolour from his Blue Period, and nine cubist works which experts believe are worth 30m euro (£24.5m) alone.
Also in the collection are portraits of his first wife Olga, as well as a number of gouaches and lithographs.
Mr and Mrs Le Guennec were initially released without charge while an investigation was launched to establish how they had come by the paintings, but eight months later they were formally charged.
If convicted, the couple face up to five years in prison and a 375,000 Euro (£278,000) fine for concealing stolen goods.