In that context you're probably right. (At the time when this was wirtten, people tended to spray initial capitals around fairly indiscriminately. Today, I think most people - not just speakers of BE! - would assume that that 'the Commonwealth' was 'the British Commonwealth' (once a sort of reality, as a PC translation of 'the British Empire', but now preserved mainly in expressions like 'Commonwealth Games').)
Another usage, among students of British history, refers to the time when the UK was getting by without a monarchy, and Cromwell was 'the Lord Protector'. (But English history is more or less a closed book to me, so check.)
PS I was coming back to add a retraction along the lines K suggests in the next post.
Student or Learner