Hey George. Can you post a link to that score or story please?? Thank you sir!
Sure. The score was listed in the old Japanese gaming magazine called MICOM BASIC. This was a popular magazine in Japan that was published from around 1982-2003. They had a scoreboard in the magazine, largely of older games. There's another list of Japanese scores from the magazine GAMEST (formerly named Arcadia) which mostly has newer games including a bunch of shmups and Neo-Geo games. The scores from both magazines were meticulously translated, compiled into web page format, and maintained by the Italian gamer GHEMANT
Here's a link directly to the MICOM BASIC scoreboard: http://stormoid.com/gamest/pregamest.html
Here's a link to the parent page that has some more explanation: http://stormoid.com/gamest/gamest.html
The GAMEST list of scores generally has a solid reputation with "real" scores. I'm not so sure how trustworthy the MICOM scores are though. The parent page I listed above says:
Before the advent of Gamest, and 'been a computer magazine that dealt with the subject of the records relating to arcade games. This magazine, called BASIC MYCOM MAGAZINE (1982 ~ 2003) commonly referred to "BA-MAGA" published monthly a certain number of records made ??of very old games. What follows' the database of data retrieved from this newspaper. We want to point out that probably many of these records have not been verified, and therefore we can define them the most reliable. Thank OLD GAME ASSEMBLE for allowing us to publish this material that we have appropriately translated ..
So I heard back from Italian gamer GHEMANT and Japanese gamer Novice with some more information on this.
The 50M score was listed in the September 1984 issue of the Japanese Micom Basic magazine. Here are the details that were given: “Mario Brothers”: 50,139,410 pts; player: 高田 and 井原 (maybe is a tag team?); game center: プレイシティキャロットガムガム (PLAY CITY CARROT GUM GUM); date: September 1984. It's listed in a section of the magazine that lists top score achievements by game center (i.e. arcade).
However the score is not listed in the "official records" in that same September issue, and Mario Bros was no longer listed in the "official records" after that. It had been listed in the August 1984 issue and prior issues. It's not clear why Mario Bros scores stopped being listed in the "official records" starting in September. It could be that a scoring exploit bug, an infinite pattern, or another problem was discovered in September, resulting in scores no longer being accepted and archived starting from September 1984.
Regardless, the fact that TWO players are listed in the details on the 50M score makes me think it is safe to discount as a single player score. Perhaps it was a tag team score, although 50M with the limited lives you get on the known Japanese romsets would still be very difficult but could at least explain the possibility of a 50+ hour game. And perhaps some scoring exploit was discovered, maybe a glitch of some kind or a way to keep getting extra lives after 1M.
Here's a link to a picture of the score from the Sept 1984 magazine: http://imgur.com/a/d64bv
Here's a link to earlier Micom score listings on Mario Bros from August 1984 and earlier when the game was still included in the "official records" list. The top listed score was 3,819,230: http://www.north-wind.ne.jp/~yoshino/challehigh/database.cgi?equal4=%83%7D%83%8A%83%49%83%75%83%89%83%55%81%5B%83%59