bash scripting STDIN over | pipe, vs. Argument $1 confusion

#Problem. STDIN over | pipe, vs. Argument $1 confusion

#This works (for one argument):
bash$: dofunction2 'RaidZ-2TBx3/1'

#This does not (for multiple lines):
bash$: getfunction1 | dofunction2

#Works:

diffsnapshotadjacentpairsA() {
	getsnapshotadjacentpairs $1 | zfsdiffawksnapshot
}

#first export(including subfunctions):
export -f diffsnapshotadjacentpairsA zfsdiffawksnapshot getsnapshotadjacentpairs getzfssnapshots
#Argument:
diffsnapshotadjacentpairsA 'RaidZ-2TBx3/1'
#STDIN:
getzfsdatasets | grep 'RaidZ-2TBx3/1' | xargs -I {} bash -c 'diffsnapshotadjacentpairsA "$1"' _ {}

#Works:

diffsnapshotadjacentpairsB() {
        if (($#)); then
            getsnapshotadjacentpairs $1 | zfsdiffawksnapshot
        else while read -r; do
            getsnapshotadjacentpairs $REPLY | zfsdiffawksnapshot
        done; fi
}

#Argument:
diffsnapshotadjacentpairsB 'RaidZ-2TBx3/1'
#STDIN:
getzfsdatasets | grep 'RaidZ-2TBx3/1' | diffsnapshotadjacentpairsB