Albs, after KwikShit condemned my front discs (felt ok to me) and wanted £260 or so to replace them, pointing to the lip, I felt the swept surfaces and they seemed ok to me, so I said "Forget it, at that price!". They looked shocked, because seemingly I "did a Lizzie" and refused to be conned.
Anyway, the real point is that I then went to Tyre-Smart for tyres and a second opinion, and they said that the discs were fine and the lip was not a problem because it's common once the discs have worn even by a small amount and even new pads wont touch it.
As you implied when you said that you would check the thickness, so long as they are above the minimum required thickness, all is well.
Ron.