Maybe Ls and Rs are interchangeable with Lss and Rss...
Not for the Realiser A16.
The labels listed in the specific listening rooms are mandarory. The tables in the appendix have some errors, for example the 7.1.4 you listed above misses the top rear speakers.
When the manual came out and I had my A16 I've been going through all listening rooms in the Realiser and wrote down all the differences to the manual, and sent the list to Smyth (list with all manual errors I found is in the thread linked in my signature).
As far as I saw the listening rooms in the Realiser seemed to be correct, only the manual has errors.
Concerning Dolby: When at first there was only 5.1, there were only surround speakers, ideally somewhere slightly behind the listener, at 100 to 120 degrees.
Then 7.1 came out, and those surrounds got the side surrounds, and rear or back surrounds where added.
If a 5.1 signal is played on a 7.1 system, the signal of the surrounds now just go to the (now) side surrounds only, without upmixing..
Therefore I think Dolby kept the labels of those speakers as Ls and Rs.
As you see DTS seems to use different labels. Since you want to use same virtual speakers with different sound formats in the Realiser they had to find a compromise. So a 7.x room in Dolby, Dts and PCM all have the same labels for the ear level speakers, L C R SW Lss Rss Lb Rb. True even up to 9.1.6, with Lw Rw (the wides which normal DTSX doesn't use, and the Dolby Surround upmixer doesn't use) and Ltf Rtf Ltm Rtm Ltr Rtr (where DTSX doesn't use the top mids).
In 5.x configurations the surrounds for all format are labeled Ls and Rs. They should be ideally at a different angle. However angle recommendations are totally wild throughout the formats, and the table in the Realiser appendix is not "correct" either.
My guideline is always side surrounds at 90, back surrounds at 150 and surrounds for 5.1 at 120 degrees, so between sides and backs.
This is why we created in a PRIR session in Jan. last year a virtual speaker every 30 deg.
So we had dedicated surrounds for 5.1 at 120 deg.
A compromise for a 7.x setup is to have the side surrounds at about 100-110 deg max, so if a 5.1 signal is played without upmixing the surround signal only goes to the side surrounds and you still will have some envelopment behind you.
Even with upmixing (at least from the Dolby surround upmixer) there will be no phantom source between sides and backs, the majority of the surround sound of a 5.1 signal comes from the side surrounds. Only parts of the signal that are somehow on both surrounds will be played by th backs.
I think the DTS upmixer does a better job here but I'm not sure. I read about this and suppose my Bluray (Pana 424 UHD) player does this automatically. I set it to convert DTS to PCM because the realiser still don't decode DTS and even with a 5.1 master it delivers 7.1 where there seems to be more mixed to the backs than the Dolby upmixer does.
PS: And always keep in mind that, unfortunately, we can not change the label of a virtual speaker in a PRIR after recording.
A Ls or Rs will always be Ls or Rs and can not be used in 7.x. setups etc.!
I suppose it would have been not so hard to implement a function for relabeling or copying virtual speakers, which would come in handy, esp. for the 24 ch versions where you have speakers like Lrs1 and so on, and if they are ear enough to let's say a recorded Ls, you then just could duplicate and relabel that speaker and use it.
I suppose Stephen could do this on his PC. Would be strange if not.
But he didn't implement it for the users though.