I am in the process of loading a new laptop from scratch and am (still) in the process of loading in my various sound libraries.
Among my biggest concerns was to come up with some effective way to determine 
1) which Calkwalk plug-ins to load and
2) which of my Native Instrument Libs/Instruments to load.
 
#1 was addresses in this thread
Is there a list of plugins from previous Sonar versions or Cakewalk Daws worth installing?


for #2 if found the following link which was a wonderful resource: 
The Complete History of Komplete - All Native Instruments Komplete Versions Compared
 
 
 
The Native Instruments Komplete Version Comparison spreadsheet it contains is a treasure.

And what did you decide regarding your second question, TS ?

Aren't all the samples/sounds backward compatible with the newest synths/samplers? At least that's what my impression was and I've been saving all the older samples/instruments (i.e. Kontakt 3 & 4 sounds) in my samples drive. Just using them with the current version(s) of synths/samplers etc...    

Mesh
Aren't all the samples/sounds backward compatible with the newest synths/samplers? At least that's what my impression was and I've been saving all the older samples/instruments (i.e. Kontakt 3 & 4 sounds) in my samples drive. Just using them with the current version(s) of synths/samplers etc...    

Even my Kompakt version (Native Instruments) of EWQL Silver works in Kontakt, and it's older
then dirt...so as far as I know yes they are....

cclarry

Mesh
Aren't all the samples/sounds backward compatible with the newest synths/samplers? At least that's what my impression was and I've been saving all the older samples/instruments (i.e. Kontakt 3 & 4 sounds) in my samples drive. Just using them with the current version(s) of synths/samplers etc...    

Even my Kompakt version (Native Instruments) of EWQL Silver works in Kontakt, and it's older
then dirt...so as far as I know yes they are....

I installed the latest version I owned, which is Komplete 9 Ultimate, and then back filled using the article's information to specifically install the missing pieces I was interested in (B4ii, SuperCharger, RC_24, RC_48, etc). This saved me hours of time.
 
From what I see the older library content is still present in the current libraries though some stuff, like the older pianos, have been redistributed and rebranded. 
Quoting from the article:

• The Akoustik Piano and Elektrik Piano Kontakt instruments that appeared in Komplete releases between 2005 and 2007 were discontinued, however most of their samples were reused in other Kontakt piano instruments that are still available today (and included in current Komplete Ultimate releases). The four real electric pianos sampled for Elektrik Piano were the Fender Rhodes MK I and MK II, Hohner Clavinet E7 and Wurlitzer A 200. These instruments now appear in the Band > Electric Pianos folder of the Kontakt Factory Library. 
• The contents of the Classic Piano Collection appeared in all Komplete bundles from Komplete 7 through Komplete 9 Ultimate. The samples used in these instruments come from the discontinued Akoustik Piano product, although any references to the original manufacturers and piano models were removed from the Piano Collection versions. The original pianos used for Akoustik Piano were the Steinway D, Bechstein D 280, and Boesendorfer 290 Imperial, and the charismatic Steingraeber 130. In Kontakt, the new instruments appeared as individual products in the Library tab as New York Concert Grand, Vienna Concert Grand, Berlin Concert Grand, and simply Upright Piano. These products were discontinued in 2014 in favor of the new pianos that debut in Komplete 10.