1991sw I explained that twice on the deleted thread !
It means the statements of the witnesses did not match so that part of the evidence is not good. (It would be 'good' if all 3 matched exactly.)
But, as I also explained at least three times, this case WILL NOT depend on the statements of 3 witnesses, who as you say are all unreliable, untrustworthy or involved in some way.
There is other far more reliable evidence in the form of DNA.
Your BF's blood stained clothing and the bar that was used as a weapon both have DNA on or in them. That DNA will have been analysed, it will prove who's blood it was and the DNA traces on the bar will prove who touched or handled it. If your BF touched the bar then his DNA will be on it, if he did not touch it then his DNA will not be on it. Very simple but very efficient and reliable. (unlike a witness with a grudge! )
Your BF's barrister will have seen the DNA evidence that is going to be presented. I am pretty sure that is a main reason he advised a guilty plea to S20.
If your BF had been sufficiently sensible to accept the guilty plea to S20 he almost certainly would not have been sentenced to more time in jail. He would be sentenced to'time served' . That means the time he has spent on remand would be counted as his sentence and he would be released after the trial. But he has decided to plead not guilty and go for a full trial on the S18. Being found guilty to S18 is ALWAYS a jail sentence of several years!
I told you all of this on the deleted post but you chose not to listen!