Yes, 0L5555 would be a Mk. I rifle made in the autumn of 1941.
If a rifle's receiver was scrapped, its serial number might be applied to a new replacement receiver, so it could be possible for a Mk. I* rifle with a post -1941 date to have a serial number from an earlier rifle.
That is not the case with that auction prize though. Sure hope the buyer was happy with the $3750 plus commission, plus tax that he paid. Including delivery, the total would be scaring 5 grand. Putting together a quality representative specimen from components gathered from here and there isn't cheap these days, but the better part of $5000?
Sure hope he knew exactly what he was buying.
A buyer has to know what he is buying.
The Long Branch .22 that is the topic of this thread is a nice looking rifle, and could be a good purchase for someone who understands what it is.