Once you are read by a company, for the most part, they will give your script on two different criteria. First, let me tell you that if you don't know what coverage is, go to www.scriptcoverage.com and you will be able to see basically the format of what coverage looks like. Disregard the synopsis and the development comments, and look at second grid at the pop of the page. Each script and reader is given a pass, consider, or recommend.
They will give a pass, consider, recommend to the script. A script getting passed at a company means very little, except that that specific company doesn't think that script would be a good fit for their company. Possibly you sent a good quality romantic comedy script to a horror company or a slasher flick to an arthouse producer. Many times even if a script is amazing, a producer can't use it, even if they enjoy it. The real important grade they give you is-
The reader will also give a pass, consider, recommend to you, the writer. This is incredibly important because if you get a PASS, they will NOT read you again. Basically, the bad script burns a future bridge.
So, if you send out a great script to 50 companies and it doesn't sell, but all the companies thought it was well-written, you can submit other material to the company. But, if you send out a terrible script, you will be shooting yourself in the foot. Which is why it's incredibly important to VET your scripts with friends, writer's groups, mentors, proteges, and everyone who can give you accurate opinions on your scripts, before you send it out to people. Because whether someone buys your script of not, if they think you're a good writer, the door becomes a little easier to kick in the next time.