BL14902 is highly likely the part number. RR is typically Rolls Royce. RR633 is more likely to be an engine type rather than a Rolls Royce Material Specification i.e what alloy the blade is made from, but for the life of me I can't remember when the MSRR system came in.
"K4222K" doesn't mean anything within the context given. Could be anything from a MOD to a repair.
The "notch" in the fir tree root is likely a deliberately machined mark to show the component is scrap and thus not to be fitted.
Additional photos with a rule to show size might help, along with a couple of different views.
Perhaps you might try emailing RR heritage to see if they can help. Bristol is the best bet.