The content is slightly different from the 1975 original. What are the rules for determining a new entry or a re-entry?

Album re-issues are counted as re-entries when they contain 100% of the original tracklist, so if it does that, then it's fine to be combined. I've just looked at the Pink Floyd album (I'm not familiar with it), and it still has the original album alongside all the additional tracks, therefore it's counted as a re-entry under this rule.

Albums that include 60% or more of the original tracklist, where certain songs are switched out for alternate versions of the same song, can also be combined. An example of this is S Club 7's '7' album, which added a couple of new songs on a re-issue, as well as swapping out the album version of Natural for the single version. Likewise, Alexandra Burke's Overcome re-issue also switched out the album versions of Broken Heels, All Night Long and The Silence for their single mixes.

Remix and live albums don't get combined, they would be new entries, unless they're sold in a package with the original album (like Charli xcx's BRAT and its remix album, which only charted separately when it got a standalone vinyl release).

It's all explained in full in the chart rules PDF from the OCC website: https://www.officialcharts.com/sites/default/files/2023-08/Official%20UK%20Album%20Chart%20Rules%20August%202023.pdf

16 minutes ago, JosephCarey said:

Album re-issues are counted as re-entries when they contain 100% of the original tracklist, so if it does that, then it's fine to be combined. I've just looked at the Pink Floyd album (I'm not familiar with it), and it still has the original album alongside all the additional tracks, therefore it's counted as a re-entry under this rule.

Albums that include 60% or more of the original tracklist, where certain songs are switched out for alternate versions of the same song, can also be combined. An example of this is S Club 7's '7' album, which added a couple of new songs on a re-issue, as well as swapping out the album version of Natural for the single version. Likewise, Alexandra Burke's Overcome re-issue also switched out the album versions of Broken Heels, All Night Long and The Silence for their single mixes.

Remix and live albums don't get combined, they would be new entries, unless they're sold in a package with the original album (like Charli xcx's BRAT and its remix album, which only charted separately when it got a standalone vinyl release).

It's all explained in full in the chart rules PDF from the OCC website: https://www.officialcharts.com/sites/default/files/2023-08/Official%20UK%20Album%20Chart%20Rules%20August%202023.pdf

Strangely the Rolling Stones' reissues of Goats Head Soup and Exile On Main St. are not counted as re-entries and actually count towards their number one tally! I think George Michael's Older reissue from 2022 also counted as a new entry on their database. They are on different labels to the original releases though so that may have something to do with it.

2 minutes ago, gasman449 said:

Strangely the Rolling Stones' reissues of Goats Head Soup and Exile On Main St. are not counted as re-entries and actually count towards their number one tally! I think George Michael's Older reissue from 2022 also counted as a new entry on their database. They are on different labels to the original releases though so that may have something to do with it.

Yes I think that's another sticking point - re-issues on different labels will count separately. Also works that way in the singles chart, it's why, for example, John Lennon's Happy Xmas displays as having a peak of #18 because its digital release is listed under a different label to the original.