There are tolerances for tile lippage. The ANSI A108.02 standards say that acceptable lippage for floor tiles with a grout joint width of 1/16" to less than 1/4" is 1/32" plus the allowable inherent warpage of the tile. If the grout joint width is 1/4" or greater, then the allowable warpage is 1/16" plus the allowable inherent warpage of the tile. Allowable warpage per ANSI A137.1 depends on the type of tile, but ranges from approximately 1/32" to 3/32". So 1/32" warpage plus 1/32" equals 1/16" allowable warpage for most tiles with some exceptions.
Note that the standards also say that the actual grout joint width should be at least three times the actual variation of facial dimensions of the tile supplied. It also says that for tiles with any side greater than 15" installed in an offset pattern (called running bond or broken joint pattern) that the grout joint width should be a minimum of 1/8" for rectified tiles (more precisely sized by grinding) and a minimum of 3/16" for calibrated tiles (not rectified). Plus it says for tiles that have at least one side 18" in length that they should not be offset more than 1/3 or you can get excessive lippage.
Excessive lippage can be caused by poor workmanship, excessive warpage or thickness variation in the tile, the substrate surface being too irregular, the tile being installed in an offset greater than 1/3 for tiles with edges greater than 18", and the grout joints being too narrow.
Perceived or apparent lippage is a condition where in fact the tile installation meets the standards and does not have excessive lippage, but appears to have excessive lippage. This can be caused by natural or manufactured lighting emanating from an angle that accentuates the lippage by creating a shaded edge. Highly reflective surfaces can compound this condition making it appear to be excessive lippage when it isn't.
I hope this answers your question.