RN curls on stripes

Could anybody dispel the myth (as some would have it) regarding wearing the curl and not the MN diamond on stripes?
I was led to believe that BSL amongst other Liner companies were allowed to wear the curl on their stripes because of the number of ships that were lost during WWII.
It appeared that it was not company wide as you had both MN diamond and RN curl, but optional.
Was there any other reason for this option?
Was it part of BSL's livery from the days of the passenger ships ?
I was led to believe that BSL amongst other Liner companies were allowed to wear the curl on their stripes because of the number of ships that were lost during WWII.
It appeared that it was not company wide as you had both MN diamond and RN curl, but optional.
Was there any other reason for this option?
Was it part of BSL's livery from the days of the passenger ships ?