Every air force had different policies and practices. There was no uniformity of this sort of thing in WW1 or WW2.
In the RAF, yes, 4 and 1/2 and another 1/2 would could be counted either as 5 kills or 6 victories (4 and 2 shared).
In the Luftwaffe, they didnt use fractions, and it would be decided to award the kill to who they thought was the most responsible for it.
In the Russian VVS they awarded shared kills as group kills, with the unit getting credit.
In the USAAF they used fractions as well, you could get 1/4 of a share.
In the IJN and IJAAF they also did not use fractions.
...so it all depended.