For those who might want to keep the offline installers for the current version of The Witcher 3 in order to be sure that they can avoid the next gen update and reinstall the latest original version any time in the future I offer MD5 hashes that allow you to check if all your downloads are OK without the need to install the game from these installers now.

MD5 hashes are:

321ed8cc0faedb903190a708686a1b50 setup_the_witcher_3_wild_hunt_goty_1.31_(a)_(9709).exe
8aab6124c22f1360585ee2285ea6d8f7 setup_the_witcher_3_wild_hunt_goty_1.31_(a)_(9709)-1.bin
3966e84f941b9fba384eb4a2b0b23c65 setup_the_witcher_3_wild_hunt_goty_1.31_(a)_(9709)-2.bin
bc80aa6b1538ecf757e7db6f3723e056 setup_the_witcher_3_wild_hunt_goty_1.31_(a)_(9709)-3.bin
71660541a0c358ef40802ba62a2c3c09 setup_the_witcher_3_wild_hunt_goty_1.31_(a)_(9709)-4.bin
9ad56c2efc7b09f480f7f8c7922c8b3f setup_the_witcher_3_wild_hunt_goty_1.31_(a)_(9709)-5.bin
bd3699654b2e34668445219f2bbbc793 setup_the_witcher_3_wild_hunt_goty_1.31_(a)_(9709)-6.bin
1beb5a622e6695d0dd65cac5fab08793 setup_the_witcher_3_wild_hunt_goty_1.31_(a)_(9709)-7.bin
121adc43111562e354d9841800d0c613 setup_the_witcher_3_wild_hunt_goty_1.31_(a)_(9709)-8.bin
0f5329306515d6f41a1b4a7b2d38ad74 setup_the_witcher_3_wild_hunt_goty_1.31_(a)_(9709)-9.bin
63e85102f7d89ca0b3271e8720def648 patch_the_witcher_3_wild_hunt_-_game_of_the_year_edition_1.31_(A)_to_1.32.exe

You can use the built-in Windows utility to check the MD5. Open the Windows command line in the folder where you saved your offline installer files and for each file execute:

certutil -hashfile <file_name> MD5

The produced value should match the value above (it is enough to compare the several first and last characters as each change in the file would produce a completely different hash).

This aged well, very handy right about now.
Thanks!