OP wrote:
"I currently have El Capitan installed and wish to upgrade to Sierra. I currently have a few older applications with licence numbers installed which I would like to continue using on Sierra. I am unable to obtain the original installation software for these as they are so out of date.."
My advice is simple:
Stay where you are, unless you are willing to risk "breaking what you have".
If the install you have now "works for you" -- well, don't mess with it.
There really isn't much more to say.
However, I will make a suggestion.
If you try this, you don't "endanger" ANYTHING on your current install.
And it -might- work.
You must follow these instructions carefully.
1. You'll need an external drive (can be HDD or SSD)
2. You'll need CarbonCopyCloner (free to download and use for 30 days):
http://www.bombich.com/download.html
3. Initialize the external drive to HFS+ with journaling enabled.
4. Use CCC to clone the contents of your INTERNAL drive to the external drive.
5. Now, BOOT UP from the external drive (it will "look just like" your internal drive, you go to the Apple menu and choose "about this Mac" to see that you're actually booted up from it.)
6. Try your old apps to see if they still run. Check every one. Do they run?
7. If yes, you can now try updating the EXTERNAL drive to Low Sierra. And then, see what it does for the apps. Be careful -- don't install to your internal drive!
The reason you want to do it this way:
If the upgrade "breaks the apps", you can just erase it and go back to your El Cap install...