Integrate EIA 923 Schedule 6_7 Source and Disposition data

[zaneselvans]

Looking at the EIA-923 archives, the schedule 6-7 spreadsheet starts showing up in 2011 and it's a separate workbook that we'll probably need to map. Looking at DOI 10.5281/zenodo.21535857 (the current EIA-923 archive as of 2026-08-17):

Year	File
2011	EIA923_Schedules_6_7_NU_SourceNDisposition_2011_Final_Revision.xlsx
2012	EIA923_Schedules_6_7_NU_SourceNDisposition_2012_Final_Revision.xlsx
2013	EIA923_Schedules_6_7_NU_SourceNDisposition_2013_Final.xlsx
2014	EIA923_Schedules_6_7_NU_SourceNDisposition_2014_Final_Revision.xlsx
2015	EIA923_Schedules_6_7_NU_SourceNDisposition_2015_Final_Revision.xlsx
2016	EIA923_Schedules_6_7_NU_SourceNDisposition_2016_Final_Revision.xlsx
2017	EIA923_Schedules_6_7_NU_SourceNDisposition_2017_Final_Revision.xlsx
2018	EIA923_Schedules_6_7_NU_SourceNDisposition_2018_Final_Revision.xlsx
2019	EIA923_Schedules_6_7_NU_SourceNDisposition_2019_Final_Revision.xlsx
2020	EIA923_Schedules_6_7_NU_SourceNDisposition_2020_Final_Revision.xlsx
2021	EIA923_Schedules_6_7_NU_SourceNDisposition_2021_Final_Revision.xlsx
2022	EIA923_Schedules_6_7_NU_SourceNDisposition_2022_Final_Revision.xlsx
2023	EIA923_Schedules_6_7_NU_SourceNDisposition_2023_Final_Revision.xlsx
2024	EIA923_Schedules_6_7_NU_SourceNDisposition_2024_Final.xlsx
2025	EIA923_Schedules_6_7_NU_SourceNDisposition_2025_Early_Release_30JUN2026.xlsx

• We'll need to update src/pudl/package_data/eia923/file_map.csv to define new pages for each of the sheets that shows up in the schedule 6-7 workbook that we want to extract, and indicates by year which file they can be found in.
• Similarly page_map.csv needs to be updated to indicate which sheet in that file contains that page's data.
• Then we'll need to create new column maps that unify all of the different normalized column names across all the years of data by page.

[zaneselvans]

@giovannicozzolongo if you want to comment on this issue I can add you as the assignee -- and we can accumulate some notes in here about the new table or tables and the input spreadsheets.

[giovannicozzolongo]

Thanks, please go ahead and assign it to me.