What is The Difference Between "Read Bootloader Code" and "Fastboot Unlock".?

hey guys and supporters..

if i unlock "Bootloader By Code" (fastboot oem unlock "BL KEY" ) device is not accepting any fastboot command like this;

Bootloader code 6318XXXXXXXXXXX

Code:

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fastboot_adb(1.0.32)_071114_r21>fastboot flash cache cache.img
target reported max download size of 471859200 bytes
sending 'cache' (6200 KB)...
OKAY [  0.180s]
writing 'cache'...
FAILED (remote: Command not allowed)
finished. total time: 0.190s

fastboot_adb(1.0.32)_071114_r21>fastboot flash frp frp.img

target reported max download size of 471859200 bytes
sending 'frp' (768 KB)...
OKAY [  0.030s]
writing 'frp'...
FAILED (remote: Command not allowed)
finished. total time: 0.040s

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but if i use the direct "Unlock Fastboot" option on software i can flash it but at this time i cannot relock the bootloader;

2019-03-05 12:10:13.869 Read from server success!
2019-03-05 12:10:14.179 Fastboot unlock done!
2019-03-05 12:10:14.189 Job finished!

Code:

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fastboot_adb(1.0.32)_071114_r21>fastboot flash cache cache.img
target reported max download size of 471859200 bytes
sending 'cache' (6200 KB)...
OKAY [  0.180s]
writing 'cache'...
OKAY [  0.060s]
finished. total time: 0.240s

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after that i m trying to relock the bootloader but this is the result;


FAILED (remote: stat not match)
finished. total time: 0.010s