If I were to take a Linux distribution (e.g. Debian, Ubuntu, etc.) and distribute their provided ISO verbatim, would I be required to provide the respective source code for all GPL software on the said ISO?

From my understanding of the GPLv2, simply stating that the software source code may be acquired from the respective Linux distribution organization would not be sufficient; rather a request for GPLv2 source code must be explicitly fulfilled by the distributor.

Is my understanding correct? What occurs if I perform a software upgrade before distributing the distro (e.g. apt upgrade) -- would the source code correlating to the updated software versions be required rather than the source code for the software versions on the ISO?

See also

Why do some GNU distributions with a Linux kernel convey GPL software online without providing source code?