> You absolutely cannot remove copyright notices from GPL software and claim credit for it.
There is nothing in the GPL that requires preserving upstream copyright notices in downstream modified versions of software, or any other form of attribution of the origin of modified versions; it does require "appropriate copyright notice", but since copyright on a derived work rests with the creator of the derivative, the modifiers copyright would appear to suffice for that for modified works. The GPL explicitly prohibits attributing modified works to the creators of the upstream work (as it requires you to include notification of your modification and a relevant date).
provided that you conspicuously and appropriately publish on each copy an appropriate copyright notice; keep intact all notices stating that this License and any non-permissive terms added in accord with section 7 apply to the code; keep intact all notices of the absence of any warranty
Removing notices can be very dangerous, and should not be done without legal advice. The default way to include GPL is to also have an absence of warranty, which is explicitly required to keep intact in modified version.
There is nothing in the GPL that requires preserving upstream copyright notices in downstream modified versions of software, or any other form of attribution of the origin of modified versions; it does require "appropriate copyright notice", but since copyright on a derived work rests with the creator of the derivative, the modifiers copyright would appear to suffice for that for modified works. The GPL explicitly prohibits attributing modified works to the creators of the upstream work (as it requires you to include notification of your modification and a relevant date).