That is normal. Patches nowadays do not contain the new files, but only the information of how to alter the old files in order to create the new ones. (called "Delta").

But: of course they don't contain the information of how to alter the new files to get the old file back (When the patch says "Make this red", it doesn't care what the previous colour was, the aim is to make something that wasn't red before, but should have been).

That's why, if you want to have the older version back, you have to completely re-download all files that have been altered by the patch, in this case amounting to 43 GB worth of files.