Can't remember what subject this came under before, but recently managed to check up on details on when detailed accident descriptions of accidents ceased.
The microfilms of HMSO publications I formerly had access to had reports for the different districts which all included tables listing all fatal accidents in detail including names, date, time, time since start of shift, & details of accident. These covered 1920-1926 after which the detailed reports of every fatality ceased.
It seems different reports where published in different ways. The House of Commons/Parliamentary Papers available online if you have access through ATHENS included all the IofM reports for earlier years, but by 1920 only a general summary and apparently not the detailed 1920-1926 reports.

The Inspectors' divisional reports ceased to be sessional papers after 1920 and hence will not usually feature in collections of British Parliamentary Papers after that year, being Departmental Publications. I'm not sure whether the national summary continued to be a sessional paper or not but I think that it too became a Departmental Publication.

Curiously, the 'full' published reports for the south Wales inspection districts that I have consulted ceased after 1914 to list the individual fatal accidents in the manner you outline. From 1914 this was an omission to conserve resources in war time. The 1919 and 1920 reports were closer to the old, pre-1914 format but omitted the detail to lescribe, and after the reports became departmental publications in 1921 the old level of detail did not resume.

There was however differences in detail between individual inspectors, with at least some inspectors of English divisions continuing to provide the old, pre-1914 level of detail into the 1920s.

You seem to state that you have encountered two sorts of reprts for the same divisions for the early 1920s. Or am I misunderstanding you? The sets I have consulted are those held by the National Museum of Wales and by Swansea University. I have compared them to the Bibliography of the British Coal Industry which is very complete, especially with reagrd to Inspectorate and similar publications, and have never encountered a further, more detailed set of divisional reports.

SAny enlightenment you can provide would be gratefully received!

Unfortunately I am unable to check this now as the source I used locally seems is no longer available. I made fairly extensive notes re particular mines I was interested in many years ago, but nothing came up for anything in S. Wales. I had assumed that because there were detailed reports for, for instance, North Wales & the South West, that these reports were similar for all areas. Shouldn't assume anything I suppose.

Thanks Alasdair. The degree of differnce between the different inspectorate divisions with regard to structure of reports and details included / omitted can be quite striking. Although after the mid 1890s the degree of conformity between divisions increased, and especially after the appointment of the first Chief Inspector of Mines, there remained significant differences, even into the inter-war period, with the ommision of fatal accident details in some divisional reports compared to the continuity of detail in other divisional reports being the most obvious difference.

Checked up on the national sumary reports for the post-1920 period (entitled "Annual Report of the Secretary of State for Mines & H.M.Chief Inspector of Mines") - they were not sessional papers; they were departmental publications. Hence they will not be found amongst sets (or microfilms) of British Parliamentary Papers after 1920.