If you look at the band's early history, Pink Floyd was originally called "the Pink Floyd Sound" until some time in 1966 when one of their manager's, Peter Jenner, suggested that they drop "Sound" from their name to become "the Pink Floyd". And if you look at the covers of their first few singles ("Arnold Layne", "See Emily Play", "Apples And Oranges", all from 1967) the band is listed as "The Pink Floyd" on all of them, including those released in the UK and other English speaking countries. It wasn't until 1968 with the release of their single "It Would Be So Nice" that they were listed as "Pink Floyd", though their album The Piper at the Gates of Dawn was released under the "Pink Floyd" name.
As for why the band continued to be listed at "The Pink Floyd" on some releases, that's a bit harder to track down. Discogs luckily has a way to view all Pink Floyd releases that were released under the band name "The Pink Floyd". It seems like the last album released in some places under the band name "The Pink Floyd" was Atom Heart Mother (though one version of Dark Side of the Moon listed the artist as "Pink Floyd" and the producer as "The Pink Floyd"). Perhaps they didn't get the memo of the band name change? Or maybe they didn't want to confuse record buyers?
I should note though that they're not the only artist whose named varied between having a "The" and no "The" between the releases: