thread like scratches in my window?

It could be a crack.

It's the glass. Glass will actually flow with age. It's just getting old.

Steve

Heart surgery pending? Read up and prepare. Download the book $10

If they are cracks, you will see the thickness of the glass in the crack, and the cracks will continue to grow. Time and temperature will do it.

That's a myth and has been disproved. Probably started by a high school teacher with a faulty grasp, and an overactive imagination, about what 'super-cooled liquid' actually means. There's glass from the time of the Egyptians (pyramid variety) and there's no thickening at the bottom from flow.

What I read was they originally thought that old glass windows had flowed because they were thicker at bottom but current thinking is that glass at the time was uneven and they just put thicker stuff at the bottom.

As for op, I wondered if scratches were just old razor blade scratches from removing paint.

Yep, you guessed it. That's still considered good practice today.

Very possibly. That's the reason I pointed out a way to differentiate between cracks and scratches, but a deep enough scratch might as well be a crack.

Lost the op original post but wanted to say that super glue works well in some glass cracks. The mirror mounted on the wall in the bathroom cracked when I tried to push it into place. The crack was weird, I could push on it a certain direction and it would show, push on the other half and the line would disappear. I put super glue in the crack and pushed on it for a minute. Cleaned off the super glue and the crack can not be seen. It's been years, maybe 3 or 4.