Weird line checking for disc defects of my DVD Live installation

Hello Techies,
I downloaded the Iso of Xubuntu 16.04 LTS, checked it using sha256sum and I burnt it to a DVD to get a live session.
Then I booted my jalopy from the DVD and selected 'Try disc for defects'.
The very first two lines that were displayed were:

/init: line7: can't open /dev/sr0: No medium found.
They occor twice even later in the check.

Actually when the check procedure is finished the result is:

0 errors found

My question is: must I worry about

/init: line7: can't open /dev/sr0: No medium found ?

Should I download another Iso and perform a new DVD burning

or

can I rely on the Iso burnt to the DVD?

Many thanks!