Im not sure the 7.7 has a flash counter in it at all.
My S3 did and could be reset by triangle away..
The best way to do it on devices that have a flash counter is..
use odin to flash older version of Rom.eg ICS or lower JB version but for our 7.7 its ICS..
Need to root to use triangle away and first remove any custom recovery,make sure its stock recovery.
use triangle away and after reset counter dont restart tab or phone go straight to download mode..
look at download mode and check flash counter and its samsung stock firmware.
sometime it requires a few times to acheive this and after a few restarts it will stop showing stock again..
even though its been reset.another tip is to remove sim card and any SD cards whilst doing this as some reason
SD cards can somehow trigger flash counter?
Once its looking correct in download mode restart device and do a OTA update to latest firmware..
This will reset you to a new locked boot loader and you will definatley have stock rom and 0 flash counter..
to keep it this way dont root or use custom recoverys...
mainly its for newer things like the S3 im sure the 7.7 doesnt have a "locked Bootloader" but i may be wrong..
also if it doesnt have a locked boot loader its easier to do than what i typed..
you cant update OTA with root or custom recovery or non stock rom..
hope this helps its what i found with reguards to my s3 and getting it back to stock for warrenty..