Engine numbers

My 71 roadster has the letter W before and the letter P on the end of the engine number.Can anyone tell me what these mean?

"P" stands for Plumstead factory where engines were built prior to engine number 134108 - in 1969. After that number engines were built at the Wolverhampton factory, but no designation letter. If you have a production '71 Commando the engine number should be 20M3S 1xxxxx. Is it possible you have a '69 engine?

Thanks for your reply ,that could be possible ,i am starting to think my bike has been built out of several models as some other thing dont add up