Is there any difference between the provisions of an earlier collective agreement and that of the current collective agreement?

I pause, parenthetically, at this point to observe that even had the earlier collective agreement been put in evidence and shown to contain provisions identical to those here under consideration, it would not of itself avail the Union. Such provisions then in both agreements being clear and unambiguous, and assuming (although without support for the assumption) that there was a continuity of operation of the provisions from the earlier to the current agreement, I would find applicable the statement of the Earl of Halsbury, L.C. in North Eastern Railway v. Lord Hastings [1900] A.C. 260 at 263: "A variety of circumstances have been insisted upon to alter the construction which the words themselves naturally bear, but I am unable to see that either in the language used or on the construction of the whole instrument there is any room for doubt. The chief argument used to give an unnatural construction of the words is that the parties have so acted during a period of forty years that the only reasonable inference to be derived from their conduct is that they have understood and acted on their bargain in a sense different from that which the words themselves convey. I am of opinion that if this could be truly asserted it is nothing to the purpose. The words of a written instrument must be construed according to their natural meaning, and it appears to me that no amount of acting by the parties can alter or qualify words which are plain and unambiguous. So far as I am aware, no principle has ever been more universally or rigorously insisted upon than that written instruments, if they are plain and unambiguous, must be construed according to the plain and unambiguous language of the instrument itself." This, of course, does not address any question of ambiguity, which was not raised in the case as a factor in interpretation.