As to the integrity of the grooves storing them horizontally, if the vinyl is stored in paper sleeves, paper deposits will probably be encrusted into them deeper, hence you'll need some good wash. I use ultrasonic. And then switch to plastic sleeves. Other than the covers at the bottom probably suffering some visual damage, you should be fine but it will take work. Vinyl requires a lot of time to get started but once the equipment is properly setup and the records cleaned and stored in plastic sleeves, you're good to go. Also use plastic sleeves to protect the covers. A tip of mine that no one ever mentions: SLIDE THE COVERS OPENINGS IN FIRST. That way dust will never enter the covers. Simple but totally effective. And store them vertically.
Records not stored vertically for decades
I’m looking to eventually get my vinyl rig back up n running and went to get my albums and found they’ve been lying flat probably for decades in two stacks of about 75 albums in each stack. Any chance they’re still in good shape, or what damage may have been done versus being stored vertically? They’ve been in a dry, temperature-controlled basement the whole time. No way to play them right now so just hoping they might still be ok. Thanks for thoughts.