specs mismatch in datasheet of MK20DX256 k20 NXP DEVICE and software packs of keil

hello all.
i am new to arm programming. i am using keil mdk 5.33 to generate hex file to upload them to NXP k20 series microcontroller MK20DX256 .
but there is a mismatch in specs of ROM which is 256kb in data sheet and 288kb as described by software packs. i want to know if this is the reason why my led does not blink when i upload hex file to teensy board using teensy loader app
please see www.keil.com/.../ this for software pack
and www.alldatasheet.com/.../MK20DX256VLH7.html for data sheet.
thanking you in advance
I installed the support packages for device
but there is a mismatch in ROM size which in actual for this board is 256KB but support package shows 288kb .i want to know if this is the reason why my hex file does not blink led on board?

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