I'll get to the heart of the question first:  If rebuilding a hard drive to freeze frame the computer and the DAW, is there any benefit to reinstalling each version of Sonar from 8.5, X1, X2, X3, Platinum Unlimited Upgrades and doing it in chronological sequence.   The only benefit I can think of is carrying over old plugins that were part of the old packages. 
 
In my personal case I don't think digging out the old Lexicon Reverb will do me any good, but I do remember using the Bass amp sim on the Guitar Rig.
 
 
Background(Feel free to ignore in favor of the question):
 
First post from a long-time lurker.    Wish the circumstances were much better and it's regrettable I haven't had as much opportunity as I'd like to be part of the genuine "community" atmosphere of assistance and passionate  dedication to detail here.  I only fantasized about the interesting questions I would throw at the group.  This one's not so interesting.
 
 
Sonar Background:  I've owned various versions of entry-level Cakewalk software up until 2010 when I jumped in on Sonar 8.5 with a Quad Processor machine and purchased each of the subsequent Sonar upgrades up to Platinum LIfetime Upgrades.   Time constraints and work-related monkey's on my back have allowed me the money to make the upgrades, but never the time to get into the work as much as I'd like( Lots of ****in' technologically advanced demos/riffs and melodies over rhythms IMHO :-) that would have otherwise been whistled into a hand held dictation machine or cell phone ).
 
 
Anyways, I always had one serious flaw in my DAW which was that I had never installed two drives, one for the operating system and one to record onto/bulk storage.  Given the circumstances, I just had a 240 Gig SSD installed(yes, they updated it with the latest Creators Update), I did not re-image the old drive onto the new(on purpose) and plan on starting over having re-downloaded each copy of my licensed Sonar software.   The goal is after the re-installs to unplug the machine from the net and "freeze frame" Sonar and the operating system. 
 
 
On a side note, I will have a busy work schedule for many months that will keep me from working on this machine so it's kind of now or never for me.  Likewise this is eating up way too much time, at a time, that is, to say the least, not convenient(not that big of a problem and my heart truly goes out to the dedicated employees of Cakewalk at this time...been there before and saying it stinks to be in that position is an understatement.  Likewise my heart goes out to anyone with bigger problems than DAW).
 
 
So,  Install them in sequence?  Or just jump right in and start downloading Sonar Platinum from the downloader ASAP and install the others later? 

Hi, and welcome. If you don't need the plugins from the older installations, I would only install SONAR Platinum.
But if you are going to install more than one, I suggest doing it in chronological order.
All the best.

If you want the older plugs, just do a custom install from the disks.

I just rebuilt my main DAW and decided to not bother with the older versions. So far only thing missing is the older LP 64 Multi band. And yes I forgot about the Lexicon which I used a lot. 
Now I'm reluctant to install an older version as it might mess with SPLAT. 
But I'll deal with it on the day I need something, I'm finding it easier just to use the newer tools. 
 
So you really don't need to over do it but what you can do is just do a bare bones install of the old version that might have everything needed, My guess is 8.5 might be all you need. Just do the custom install and un check everything but the plug ins and VST's. 
Then install SPLAT and all it's stuff. 
 
I might just get brave today and try installing 8.5 and see if it trashes Splat. I'll set a restore point first. I think I will miss the Lexicon and LP 64. V Vocal was also cool. 
 
But I don't think there's any point in installing X1 or X2 if you have 8.5. 
Somewhere here someone posted a complete list of all versions and what they came with.
I should have bookmarked it. 
Was that Abacab? 

I just installed 8.5 bare bones, I unchecked everything but the few things I wanted and it worked without issue. 
I found Lexicon, Session drummer 3, LP 64 multi and EQ,  and a few I wasn't sure about like Sonitus. 
Just ran the VST scanner and they are now happily parked in SPlats list. 
 
So there you go, even though it is recommended to install versions in the order they were released it is not actually necessary if you just do a bare bones. 

There are a few advantages to installing older version usually has to do with a familiar work flow or feature that is not in a more recent version.
 
All of the following refers to X-Series and older versions of SONAR.
 
The SONAR installers have an advanced install option a couple of screen into the install process that provides for installing individual plug-ins. The only exception is V-Vocal which requires a minimal install of an older version of SONAR to get it. The minimal install is an option in the drop down at the top of the advanced install component pick list.
 
When performing full installs of SONAR, it is preferable to install them in chronological order - oldest first. However, the installers are pretty smart and will not overwrite newer files. This means it is not entirely necessary to perform installs in any order. The only exception I am aware of was a problem with X1 overwriting the QCEQ causing problems in newer versions. The fix was to re-run the newer version installer.
 
Here is a post containing a document of plug-ins by version

http://forum.cakewalk.com/From-X1-to-Platinum-Plugins-amp-Soft-Synths-A-Comprehensive-List-m3228689.aspx
 

I found that if I did not rebuild from my multiple versions I could not find my older Digital Sound Factory files.  And perhaps some of the legacy included VST synth plug ins.

Content usually came on Additional Content disks. IIRC, some of the Additional Content disks did check the registry for SONAR version info. It may take a minimal install (again an advanced install option) to run these installers. There is no requirement to keep the version installed after installing the content though.

Zargg
http://forum.cakewalk.com/From-X1-to-Platinum-Plugins-amp-Soft-Synths-A-Comprehensive-List-m3228689.aspx

The list I linked contains info from SONAR 3 through Platinum although I did not check it for the most recent Platinum.