Can we have some context here? Like, did you just jam eight plugs in a quarter sized hole or was it repaired three years ago without further issue and you're just checking?
A plug is (by the rubber manufacturers guild or whatever...not those rubbers, you creeps) deemed a temporary repair. That said, people have been plugging tires forever. A patch is better as you can see and cover the damage vs poking and hoping with a plug.
Bill is sort of correct. A "blowout" can be caused either by a sudden large impact and loss of pressure, but more commonly is a gradual loss then the tire overheats and fails. So if your plug works loose you get the same end result as a puncture. Modern cars with tire pressure monitoring mitigate this by giving you some warning poop has hit the fan.
Short answer, a plug repair that has been fine for some time is probably still fine. If it was an emergency repair done to get you home or close to the sidewall, maybe have it looked at before going much further. We had no major issue patching over an existing plug (if feasible) as current repair standards recommend you fill the injury channel anyway.
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