It is clear that there are issues of various newspapers missing from the iMuseum Newspapers & Publications. For example, while the Peel City Guardian is said to run from 1885 to 1960 this is not so—between 1882 and 1895, there is a sole surviving issue, that for 21 February 1885. Starting with 1895, there is a more or less complete run, though 1903 has just copies for December present, while 1905 is missing in its entirely. Within some of the others years, individual issues and certain sequences are also missing. Specifically, 1895: 19 January, 6 April, 29 April, 4 May, 11 May, 18 May, 25 May, 1 June, 8 June, 6 July, 13 July, 20 July, 1 September; 1897: 31 July; 1917: 8 September, 6 October, 27 October. [I have looked only as far as 1921]
While browsing other titles and for other years I notice too other issues are missing. This has an effect on research it goes without saying and needs to be documented. So please do post when you come across missing content.