Single Signed Baseball Qualifications

[ATP]

Hoping to get some thoughts from folks about when and what they consider "single signed " in regards to an autographed baseball Is other writing on the ball acceptable, if it's penned in the hand of someone other than the signer (ie, a notation from the owner, date, etc)? How about the owners name itself written or signed on it (assuming they are not famous themselves, I have seen this a few times most recently with a Ty Cobb ball I had). How about writing on a ball that has been obscured (worn off or can't tell if exactly what it is, other then ink marks). The reason I ask, is I am looking at a ball with one signature, and one clubhouse signature. I would think in most minds this would not qualify as single signed, but interested to hear opinions. I am sure there have been examples of Ruth clubhouse and Gehrig side panel, and that these aren't considered single signed by Gehrig (the example I am looking at isn't Ruth/Gehrig). Thanks in advance for your thoughts.