Unfortunately, I don't have the disc now, just digital version. So, I can't access my old save files. Is it? Or, I have to buy standart edition and I can use my old GOTY version progress. Also, I don't understand why the digital version and disc version of the GOTY edition are different products.
Correct, you cannot play the old saves without your old installation / disk.
Why:
Let's say I release a game. We'll call it "product 123". I release an expansion. Let's call that "product 4 for version 123". I release a second expansion. Call that "product 5 for version 123". So, as is, I need to buy 123, then 4 and/or 5.
Now, I release a GOTY edition, which is a standalone, combined package of 123+4+5 in
one download. Call this package 456. While, to a human brain, this seems logical, a computer cannot "think". So, to ensure the marketplace can differentiate buying the GOTY edition from buying the Standard Edition+DLC 1+DLC 2...it will differentiate the two purchases as two completely, different products.
On PC, this is no big issue, as PC marketplaces allow for modification / manipulation of files, etc. On the much more rigorous console / mobile marketplaces, they do not not allow such manipulation of files, as they run security checks to avoid any form of tampering / malware / viruses whenever a program is launched. So 123+4+5 will be identified as a totally separate product from 456. They will also need to be supported completely separately from each other. So, if I release a patch for 123+4+5...I must recompile and re-release a completely separate patch for 456. It hurts both ways (as studios regularly need to pay tens of thousands of dollars to release new patches / DLC content for
every individual product every time they want to release anything. This is also why support for older versions of products are discontinued.)
Hence, CDPR has gone to rather great lengths to ensure that support for players that have Standard Edition+DLC are being followed up with the updates that people playing the GOTY Edition enjoy. But nothing can change the fact that the marketplace / console OS will view them as completely separate products. (It's basically for security purposes. Which is one of the things that facilitates consoles' ease-of-use.)
In the end, it's six of one...half a dozen of another.