Please also note the samsungk9f1g08uoa_a.bin and samsungk9f1g08uoa_b_usb.bin files are 138,412,032 bytes length.
According to the device datasheet: "flash is 1Gbit with spare 32Mbit capacity."
138,412,032 bytes = 0x42000000 = 0x40000000 (1Gbit data) + 0x2000000 (32Mbit spare)
Write and erase operations on flash devices are always performed using data block to speed-up the operation. The Samsung k9f1g08uo have 0x20000 bytes block (128KByte).
This mean that every data block starting with 0xFF 0xFF 0xFF 0xFF data is unused and fully filled with 0xFF bytes.
0x00000000..0x0001FFFF - fully filled with 0xFF
0x00020000..0x0003FFFF - data
Just after merging the "samsungk9f1g08uoa_b_usb.bin" with the "samsungk9f1g08uoa_a.bin" you got your 264MBytes (128MBytes+4MBytes * 2) flash image.
Right now it seems that less then 50% of the flash image have valid data.
I will try to check it according to the einzwei's information.