[Q]What exactly is TA partition and when does it change?

Hello everyone, I did my best to help a few people in Q&A section, but now, I have a few questions myself, all of them, regarding mysterious TA partition.

My C1905 came out of the box with branded 15.1.C.2.8 firmware. One of the first things I did after rooting the device was backing up my TA partition, knowing that I will sooner or later unlock the bootloader. However, I then cross-flashed unbranded C2005 15.2.A.2.5 firmware. My questions are:

1)Do I need to backup TA partition again on a new firmware to be able to relock my bootloader without changing it? Does the TA partition vary between firmwares?

2)Will changing my firmware again to official 4.2.2 for C1905 (which should be released within 2 months) require my to back it up again? Is the C2005's TA partition different than C1905's?

3)Just out of curiousity, what exactly does the TA partition contain? From what I've read, it stores unique "DRM keys", but that doesn't tell me much. Are these keys linked with any hardware (like - for comparison - Samsung's "EFS" folder stores IMEI, MAC adress product code etc and without it, phone has very limited capabilities), or is it just more like "locked bootloader certificate"?

I just want to clear that up, thanks in advance for answering.

stamatis said:

1),2)No, you have unlocked your bootloader and your DRM keys are gone, you have them only in your back up. If you want to relock then you will restore your backup while in stock rom-kernel.

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I think you didn't fully understand the first question. Can I backup TA of my current firmware and then use that back up to relock bootloater WITHOUT changing it back to the stock 15.1.C.2.8? Or do I HAVE to roll back to stock firmware and only then I will be able to relock it? Or maybe I can use the stock backup on any firmware, because TA doesn't change? In other words, can I relock the bootloader on other ROM than stock?