Mark Jones, 45, of Cwmbran, Torfaen, has pleaded not guilty to murder at his trial at Newport Crown Court.
The jury heard Mr Jones changed his story during a series of police interviews over a number of months.
Initially, Mr Jones said he tripped over a toy and dropped Amelia Jones the day before she was taken to hospital.
He told police he dropped his granddaughter on 16 November 2012, but then said in a later interview that another person, who cannot be named for legal reasons, dropped her the following day while "messing" with their phone.
The trial has been told that baby Amelia suffered a fractured skull, brain swelling and eight rib fractures.
She had been injured at least three different times, the court heard.
The trial continues.

The device was discovered last week, southeast of Tucson, Arizona, when agents spotted a group of men scattering as they approached.
A closer look turned up two bundles of cannabis weighing a combined 47lb (21kg), which had yet to be launched.
The catapult was dismantled on the Mexican side. No arrests were made.
About 650 miles of the 1,100-mile (1,770km) border is covered by some sort of wall or fence.
Donald Trump has committed himself to building more walls, but drug traffickers have in recent years turned to increasingly creative means of getting their product over, including drones, car ramps, and air cannons.
Traffickers have also made extensive use of tunnels under the border. In March, authorities uncovered a 380m tunnel that ran from a restaurant in Mexico to a house in California.

Tigers were awaiting official clearance from the French Rugby Federation and the 30-year-old, who has won 35 Test caps, is now able to cover for injured duo Manu Tuilagi and Matt Toomua.
Head coach Aaron Mauger said: "We are missing two big players in midfield.
"We're very happy to be able to bring in a player of Maxime's style, quality and experience."
A man accused of murdering his five-week-old granddaughter said someone else dropped her the night she was taken to hospital, a court has heard.
[NEXT_CONCEPT]
US border patrol agents have found a medieval-style catapult mounted on the border wall with Mexico, designed to launch bundles of drugs into the US.
[NEXT_CONCEPT]
Leicester have completed the signing of France centre Maxime Mermoz from Toulon until the end of the season.