@diophan said in Vintage Proxy Guidelines:
@Islandswamp If you are not playing with black sleeves, in all likelihood they are not 100% opaque. In that case the back of the delvers are distinguishable and they are marked. At Champs in 2014 when delver was a common deck many people received game losses for having marked cards because of this. (Snarky comments omitted.)
There are a number of other sleeves that are not black that are completely opaque that I've seen and/or used before. It just depends on the brand, thickness, and texture. I've seen sparkly blue, purple, brand sleeves, etc that aren't black, but are completely opaque.
Regarding the original question, to my knowledge Zherbus was the first person to permit "proxy" Vintage tournaments, and the guidelines weren't very strict. The only rule was, at first, just 5 proxies.
In Columbus Meandeck Opens, we opened it up to unlimited proxies, but with common sense rules that, 1) if you used print outs, that all of your deck had to be proxied in the same manner so as not to have some cards of different thickness), and 2) to have all of the key text on cards.
In the early days of the SCG event, when they first started permitting proxies, there weren't specific rules (so text on magic card backs were permitted), but later Matt V issued more specific guidelines.
Although I've always preferred black sharpie on a magic BACK (not front) because I think it is much easier to read than trying to read sharpie on the front of a card (where other text and chiaroscuro make it harder to read), SCG eventually required all proxies on basic lands (and on the front), and I think they did so for, as others said, readability at a distance.
Because it was simply easier, I think most groups just would link to the SCG rules, and ask their player base to follow that format, so the SCG rules became a default among groups that permitted proxies. But not because it was better - just because it was codified from a reputable source.
That said, I TO'd a ton of tournaments in the mid-oughts, and don't recall anyone ever raising the concern that sharpie on the back of a card is a problem - but that may be because all of the sleeves I remember from that period (roughly 2003-2007) were virtually all completely opaque on the back. The question about curvature I don't think matters because most pack fresh cards aren't curved (which are the most likely proxy targets), and the sleeves of proxied cards and the proxied cards themselves will acquire the same curvature of the rest of the deck, to the extent that this is even an issue (and I've never heard it raised before now).
The only time I've ever heard anyone complain about curvature or warping is for foil cards (Rich Shay used to complain about this alot) or cards that have been riffle-shuffled to hell. About ten years ago I sold off nearly all of my foils because I began to be persuaded that they were more likely to be warped than regular cards. That's the only time I've ever heard anyone complain about curvature.
Of course, subsequent to that period, Magic printed both double sided cards and textless cards, so alot of the debates about card backs and the text requirement looks silly in retrospect. The simple rule of thumb should be that if a proxy is in any way identifiable from behind that the card is "marked." YMMV