Short titles for UK Parliament Acts are generally formed with the title itself and the year, e.g. Parliament Act 1911, (or, in Yes, Minister terms) Import, Export and Custom Powers (Defence) Act 1939.
Hypothetically, if there were two Parliament Acts in 1911, how would each one be cited, or, as the citations are defined in statute, what would be the standard way of defining that citation?
Where the primary part of two acts in the same year would be the same, commonly a secondary phrase is added in brackets indicating the narrow subject of the act to avoid this happening. For example, the Supply and Appropriation (Anticipation and Adjustments) Act 2016 was followed later in the year by the Supply and Appropriation (Main Estimates) Act 2016.
However, where such a secondary phrase would be inappropriate, especially where the later act replaces the earlier act, the main part of the short title of the second act is appended with "(No. 2)". One such example occurred in 2009, where the Appropriation Act 2009 was replaced by the Appropriation Act (No. 2) 2009.
So in your hypothetical case, the later act would likely have "Parliament Act (No. 2) 1911" as its short title.
I should note though that this is governed by custom, so there is no guarantee that a particular act must follow this approach.
