KKDDMM, Thanks for sharing all the photos. It's very interesting.
Where did you buy all these 9998, and v911s? The 9998 looks new. However, one flybar weight is already missing? Since you have almost all versions of the V911 Rx, you might want to compile a list of Board name, Rev, and Release Dates. I did such a reference table for the WL-V929. I noticed that the V911 did a similar thing here. The board name went from WL-4CH01R to WL-4CH02R and then they reset the Rev number.
Daryoon had already pointed out that the later Revs have replaced the cylindrical crystal with a SMD. It will make repair more difficult in the future. But I also hope that the new SMD crystal will hold up better than the cylindrical one, so that replacing it would be a moot point.
What caught my eyes was the writings on the "new" WL-4CH02R REV 01 2012.05.29 board. If you read a little bit of Kanji, you might pick up that it says: 老飞机, I think. I couldn't make out the 2nd word, because the wire was in the way. But if it is what I think it was, it means "old aircraft".
Then you also see in a couple places, where it say "Old_Sev..." Part of it is covered with white glue. It makes me wonder, why this "newest" board has all the references to "old" stuff??