Scott, maybe I can help with an example.
Here are quick and dirty green light DPAC images (you can tell by the keystoning of the lines and over exposures) taken from an old AP 127 F8 pre-ED Starfire. This lens had been modified decades ago by the, now deceased, original owner, who, for some reason, replaced the spacing oil with a cement. He did a pretty good job but the cement did not age well, putting stress on the glass, leading to a very easy to see turned edge, and some over-correction to the entire figure.
I first noticed it as a rather soft image of Saturn (but color was fine). The star test looked almost identical to the example Paul has shown. At focus, the airy disk looked ok. However, the intra and extra focal images were waaaaay different from each other, very much more so than other similar vintage APs I have. I quickly suspected a turned edge and I went right inside and made a quick 115mm aperture mask out of paper and stuck it over the objective. BINGO! The image of Saturn was much sharper with a much more normal star test (that showed over correction though). Back inside, I removed the lens block and stuck in DPAC which confirmed what I had seen visually. The images in green are attached.
So, this is an example of a lens with a very uniform, easy to detect turned edge. This one was obvious but I hope this example gives a perspective on edge issues and their subjective effects. . Like Paul says, the edge does matter.
FYI, the lens went back to AP where Roland measured the as received correction in green at a .82 Strehl. Once he separated the elements, let them "relax", re-oiled them and had another look the Strehl has improved to .93 in green, better in yellow. Roland said he could do a bit better and refigured the lens, which then came in at a .98 Strehl (though with some very narrow, circular machine polishing marks/zones that I can see in DPAC). It is now an excellent visual lens.
Edited by Jeff B, 11 February 2020 - 02:16 PM.