Dates changed on the photos

Photos were taken in 2011 on Samsung phone GT-B3310 (not a smartphone). This phone was switched off for over 2 years in 2013. * On 24 January 2015 the phone was switched on and transferred the pictures via Bluetooth onto my Samsung Galaxy S3. The pictures showed dates from 24 to 28 January 2015. Some pictures had 24, some 26, 27 and 28. The Exif file also showed the dates from 24 to 28 January 2015. The original dates in 2011 were missing. * Samsung South Korea said that if a device is switched off for long, and subsequently switched on and connected to a device (phone/computer) the pictures would take the switch off date. * But the puzzle is, why do dates vary from 24 to 28 January 2015? Can anyone kindly give answer? This has created a *huge* issue/problem for me.