There’s a random gap in my tattoo that I’ve had for 1+ years. How am I just noticing this?

I had lived in the same house for ten years when I suddenly noticed a sizable tree at the furthest corner of the front yard, trunk of about six inches in diameter that I did not know was there. In my defense, I rarely used the front door - but even so.

Not noticing things does not surprise me. Maybe how you are holding your hand emphasizes it - and you never held your hand that particular way and looked at it.