A 1/2:1 or 1:1 is very wacky (while not directly ruled out) and I doubt we ever see one.
1:1 has occurred, apparently, in English chess.
Check out the obituary for Steve Boniface on the Chess Arbiters Association site.
One year at Paignton, one of his favourite events, Steve had the evening off while the other controllers organised a blitz tournament at the playing hall. On his way back from the pub (almost certainly one that was in the CAMRA Good pub Guide) he could not resist dropping in at the hall to see how things were going. One of the controllers came running up: "We're glad you're here, Steve. There's been a dispute - could you sort it?" A boy of about ten was playing a man in his late seventies and the boy was winning easily. He got a pawn to the eighth rank and announced a queen, but not finding a queen to hand he left the pawn in situ. When on his next move he attempted to move his pawn as a queen the man claimed a win for an illegal move (they were playing the blitz rule that illegal moves lose). Steve knew the final round was being delayed and the man was adamant that he must have the win; the small boy was looking very confused. Having checked that the result would not make any difference to any prize money, Steve came up with a quick and unique solution. He took the man off to one side and informed him that he had won the game. He then did exactly the same thing with the young lad. One point each: truly a modern judgment of Solomon!
The obituary also appears on the site for the Bristol League where he played most of his chess. According to this report from the Guernsey chess festival he also had an inventive approach to pairing.
I'm not sure his arbiting decisions would meet with approval today.
1/2:1 occurs regularly although you don't see it because the pairings are changed. It happens often in the first round of a tournament like this.
- Player A requested a half point bye in the first round.
- By mistake the arbiter pairs A with B
- B sits there for half an hour until the default time expires and claims their full point
- Either the arbiter realises a mistake was made or the next day player A points out their bye request and the pairings are changed retrospectively to show player A getting a half point bye and player B getting a full point bye. If this happens to several players then you have several players appearing to get full point byes in the same round. Clearly not possible according to the rules but less embarrassing than declaring to the world that the result was 1/2:1.
This practically leaves only a 1/2:0, which is possible by §E10.2 (and §E12.9). Do you have an actual example?
This could happen where player B is disqualified for some heinous crime but opponent, player A, cannot mate by any series of legal moves. Player B definitely gets 0 but player A cannot be given 1 and so is given 1/2.