I wish I thought about this a few months back when I bottled my RIS
I think luckily there is at least one unmarked and one Sam Adams which I hear are possibly accepted sometimes.
Sometimes..check the rules for sure they will actually indicate what is allowable as bottles...including whether or not no descript etches are allowed.
This is that section from the Michigan Sate Fair Comp where over 800 beers will be judged.
Each entry must consist of two (2) bottles of between 10 and 22 oz from a single batch of beer, with no labels or identifying marks. Caps with any markings must be blackened with a marker. Commercially available bottles from widely distributed beers are acceptable. Unique bottles will only be allowed at the discretion of the Competition Organizer.
ANd the Michigan Rennaissance Festival Beer Barons Brew Brawl;
Each entry must consist of two (2) bottles from a single batch of beer,cider or mead, with no labels or identifying marks. Raised lettering on bottles is strongly discouraged, but bottles with generic raised lettering will be accepted. Caps must be plain or blacked out. Unique bottles will only be allowed at the discretion of the competition organizer.
Looks like standard cut and paste BJCP rules boilerplate.
But I got into that habit a couple years back...make sure you have at least a 6-er of every brewed batch in plain 12 ounce bottles (usually a few more than 6 but a minimum of 6)...then those I think are "worthy" of entering I set aside, those that the batches are "eh" I just drink. Then come competition deadline time (Which was last week for both of those comps I entered) I dig out the bottles (some may be a year old or more old) Chill down 1 for a few days and taste it, to make sure it is good, not infected, etc.
And then I decide which I am going to enter. I never brew "for competition" I see if what I have brewed is competition worthy. And what category to enter in. Because honestly not every beer turns out to be the style you mean it to after it has conditioned...for example a 6 month old IPA, after the hops have faded, may realistically be best called a PALE ALE now...so it is best to figure out what to put a beer into.
I even dug out a sixer of the strongest feeling plain brown bottles for my saison which was carbed at iirc 3.5 volumes of co2 and the rest of them were in champagne bottles and 22 ouncers.
I did three beers for state fair.
Vienna Lager
Chile Powder Porter (formerly called chocolate mole porter-but the chocolate has faded)
Oaked Old Bog Road Brown Ale-(1 year old)
And for the renfest I did those same ones, and the saison (I didn't really want to part with 4 bottles of this gem, and figured there would be more competition to get lost in in the State fair, and less in the renn. fest, so I figure I have a better chance at placing in that one.