Damage to tyres?

Think I might have tracked down the cause for you. Rubbing mudguard.

I'll preface my comment by highlighting I'm not a qualified bike mechanic so feel free to ignore anything I say or take it with a pinch of salt

But that disclaimer aside, I'd be happy to carry on riding those tyres, that silver reflective bit always seems to do that on tyres and Marathons are pretty solid anyway, as long as the inside is fine theyll be good to ride for a while yet imo

That's a flesh wound. I got home from a ride with this (I did notice a slight variation to ride quality). Managed to resist the temptation just to glue it down...

That white reflective tape looks like that often from new. Image one is the diagonal cut from manufacture, 2 looks like a wrinkle from manufacture and the 3rd a minor scuff. 

The marks further out - is that blue paint from the frame? Nothing though that looks bothersome to the tyre. Check the inside of the frame in case there is any scoring, but still looks fairly inconsequential.

Looks superficial to me.

What does the inside look like though? That would be more informative.