The * conversion was outside the remit of the WRS. According to Skennerton, the * upgrade was incorporated into the manufacturing process, it was not a "retro-fit".
If rebarreling was within the WRS spec, (and I'm not sure if it was) it is possible that some Mk1 rifles became "upgraded" by default if a canibalised Mk1* barrel got fitted. In such cases it wouldn't have been necessary to replace the bolt, as a Mk1 bolt will function in a Mk1* rifle. It's also a possibility, of course that the barrel was replaced post service.
FWIW, the serial number stamping on your bolt looks original to that component.