I've mentioned this in other, older, threads, but I too have never been fully deep-throated. My head is less than a 6 inch girth, but my entire shaft has a 6 inch girth, and tapers to 6.5 inches right at the base. The vast majority of the women I've been with easily take the first 3-4 inches, but only a few were able to go 5 inches or more down on me
One of the woman who came close was commenting on my size and girth as she was going down on me for the first time. She was taking me fairly deep, easily 4 inches on every stroke, so I mentioned that no woman had been able to take me all the way. She took it as a challenge and said "Let's see if I can do something about that!" She enthusiastically went deeper, likely 5+ inches, but she could get that last inch and a half down her throat. Of course every bit she took in felt fantastic, amazing and got me even harder, which didn't help her out. She gave it her best, and it made me very, very happy.
Another woman, years later also enjoyed going fairly deep when giving me head, and I mentioned the no fully deep throat "problem". She took it as a challenge as well and was able to take 51/2 inches on most strokes. Again, that little bit of extra depth always felt amazing. I ended up marrying the 2nd woman who (almost) takes me balls deep down her throat! She still hasn't taken all of me, but almost 90% is close enough for me!