Records not stored vertically for decades

@soix 

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.

You should buy a quality disc washer 

For $2-3k you should be able to get one that washes

Dries. Myself csnt be bothered with high quality digital being so good 

But disc have their own qualities my brother disc washer 

Is to me expensive over $5 k  check with

The needle doctor or others  on quality, pricing.

What fun you will have re-discovering those recordings.

Checking if flat on glass is a good idea. If not flat, a Shure cartridge with a damped brush would be a good idea.

My favorite elliptical with damped brush is M97xe

M97xe, good price

Other aftermarket stylus replacements that have brushes are not damped, like my Jico replacement for my Shure V15Vxmr. Great stylus, the brush is good, but not as good for warps as damped. 

btw, you can play these cartridges with the brush down/working or up, they simply click in up position.

My other thought is that some paper dust might be pressed in the grooves more aggressively than vertical, i.e. not easily dislodged.

My old LP's sound significantly better after a good manual scrub. I do batches of 10 at a time, the brush is a baby scalp brush from Amazon

baby scalp brush

I've had records that were stored flat for months to years and never had an issues with them.  I think as long as they weren't submitted to excessive heat or humidity they'll be fine.

So since you have about 200 albums, I would run them all thru a US RCM. That will get rid of any mould/dirt/dust, etc. The only ones I would worry about for warping are the top 5-10, since they would not have much weight on them. Vinyl is heavy, so anything under those would be fine from any warps. 

My 2 cents... Good luck and enjoy when you get everything back up and running. Lots of fun. Just finished listening to Analogue Productions Gaucho - 45 rpm - re-mastered by Bernie. Another home run if you are a SD fan.