Some stores will let you return opened media, some won't. Sometimes it just depends on if the manager feels like being a prick.
In answer to your question, dvd brands dont really mean anything, but not in the way you are thinking. the disks you got are probably cmcmage01 or philipsc08. The majority of media that you see in stores are not made by the company selling them, in fact their are relativlly few companies that actually produce media compared to the number of brands out their.
All dvd media contains a media code on the disk that identifies who the manufacture is and what model it is. Use this free program to read the media code off yours, both the ones that are not burning good and others that have burned good (you can read the code on stuff that you have already burned or blanks).
My computer seems to be a little stuborn about going to the site to get the url but just google dvd identifier.
Media codes are extreeeemly important and basically will be the deciding factor if your burns go good or not. You want to find what media codes are good, further find out what media codes work well with your burner, and you should be good to go.
Another very important thing is the firmware on your drive. The drive reads the media code and the firmware has instructions on how to burn each particular media code. If you have older firmware, which if you have never updated it, you probably do, newer firmware might very liklly fix your problem.
Go here to enter a brand and see what media codes that brand of media uses
That probably wont do you much good right now, but bookmark it as it is a very valuable database once you learn a little.
Go here to find out about your drive, firmware, and what medias work well with it.
It might look like a lot of information but spend a little time reading through it. If you post the media codes of the media you have here, I can tell you a little about them and guide you towards getting more.
Another issue you can look into is error scanning. with most drives you can scan a burn to see how well it burned (rather than does it play as that is a little ambigious plus thier are other issues with playability beyond the media quality or how well it burned).
I kept getting interupted while posting, guess you guys beat me to it while I was typing.