Pencil is a great medium for the reasons listed, but my understanding and avoidance of pencil comes from not being able to tell when a pencil signature was applied. A pencil signature signed today on century old paper will have the same characteristics as a contemporary pencil signature. But when it comes to ink, applying new ink on old paper causes all kinds of flaring in the ink transfer that you don't see in pencil. Seeing a lot of flaring on a supposedly old signature is an indication it was added later and may not be original.

True, but that's where personal knowledge and the confidence in it has to come into play. Or, like so many new(ish) people in the hobby, one can choose to never learn anything for themselves and simply buy the slab.

My comments were about the general rule of thumb. I'm not suggesting anything about TPG opinions or anything like that. Only that pencil can be applied to old paper and it can be difficult to determine if the signature is a day old or 100 years old.