Looking for SGC Authentic assistance

[tmoore_25]

I visit this site infrequently but know that this is where the majority of vintage knowledge resides. I admit that I am not very knowledgeable about the world of vintage. With that being said, I have always loved Allen & Ginter cards and have put the mini sets together from 2006-2018. I have dabbled in some of the original cards and have put together about half of the 1888 World's Smokers set. My concern is that obviously I am missing something when looking at them and clearly am out of my league with reference to alterations.

I submitted 18 of these cards to SGC for grading assuming that most all of them would get poor grades in the range of 1-4. After seeing the grades pop when they shipped today I found that 10 out of 18 were graded as AUTHENTIC.

My question is could anyone enlighten me on why they were graded this way? I know some of them have writing/ink/pen marks on the back. Does that automatically make a card ungradable? Some have stains on them. Does that make them ungradable? I'm just looking for some knowledge on the subject so that I know what to look for when I continue purchasing the remaining cards and trying to replace those that did not get a numerical grade.