Hello, Burl,
Absolutely do NOT use ANY stick-on labels at all! 😟 EVER!!!!! Even the 'expensive glossy' ones. They will damage the disk, resulting in unusable DVDs. If you like making labels yourself, get a printer that prints directly onto the DVD disks, using printable DVD-R disks.
Playback of DVDs is quite dependent on the player. Many set-top DVD players treat the DVDs differently. With commercial DVDs, this is not always a problem, probably related to how they are made. Commercial DVDs are pressed, not burned.
I have had no problems playing my burned DVDs on any of my Sony DVD players, but frequently my disks will not play correctly on our newer Toshiba DVD player. Often the Toshiba reads the audio tracks wrong and the sound is either muted or lost in parts of the movie. There is nothing wrong with the disk, it plays fine on other players.
However, you do need to be using very good media for burning, like Verbatim or Maxell, DVD-R disks, and you should be burning them at a slow burn speed, 4x or less. If you first create a disk image from your iDVD project, you can use Disk Utility for burning, and select a slower speed.
I hope you are not using Memorex disks for burning. They are known for being problematic.
Post back if you have more questions.
Meanwhile, burn more DVDs of your projects that are on plain DVD-R disks WITHOUT those stick-on labels!