Thunderbolt display firmware update 1.2 keeps reappearing, but is not compatible
I had a similar problem: The "Thunderbolt display firmware update 1.2" kept reappearing in AppStore, even though the uppdate seemed successful.

According to Apple the update was successful when the the Firmware Version is 26.2 and the Port Micro Firmware Version is 2.0.7 (visible in About this Mac -> SystemReport).

Above versions were correct in my case, but the update still kept appering in AppStore... (probably I did download and install the update manually after the first failure, but I don't remember ...)

To get rid of the annoying update in AppStore I used the softwareupdate command on the commandline:

softwareupdate --ignore TBdisplayFWUpdate1.2


The update package name may vary. For example:

softwareupdate --ignore ThunderboltFirmwareUpdate1.2


To find the correct name of the update for your machine, use the following command and copy the update package name up until the "-" 

softwareupdate -l