When your employer submitted the I-140, it represented how much work it had for you beyond your six years. If the I-140 has been approved, you should already know the period for which it was approved and whether, post-transfer, your new employer would have to file another I-140 to get approval for a greater period of time than the USCiS has approved. I would expect that when your prospective employer petitions for the transfer, it is going to refer to the existing I-140 approval and ask for a three year approval, but that's something you would have to ask them.

