As I understand,
If you have cat B, cat C1, cat C, cat D1 and D and you take your C+ E test and pass it upgrades those licenses to B+ E, C1+E, C+E, D1+E and D+E
But
If you only had cat B, cat C1 and C and you took your C+E it would obviously upgrade the entitlements you have but if you at a later date were to gain cat D and D1 would they still upgrade or would you have to take a further test to gain that entitlement?
If that makes sense… 
So basically you mean that when you pass your C+E test, they upgrade your B to BE, C1 to C1E etc, would they do the same if you then took your D test?
I believe they do yes, but the man to ask would be Dean because he just recently sat his bus test.
You would be entitled to the +E upgrade whichever way round you do them. You could do a Bus and Trailer test and have your lorry, car and minibus automatically upgraded. Also a Bus test done in an Auto after passing a Manual Lorry test automatically upgrades the bus Pass to a Manual and Vice Versa.
But make sure DVLA process it correctly as I had to send my licence back to have the missing +Es and it took them 6 weeks to adjust it because a manager has to manually verify the licence.
dar1976:
You would be entitled to the +E upgrade whichever way round you do them. You could do a Bus and Trailer test and have your lorry, car and minibus automatically upgraded. Also a Bus test done in an Auto after passing a Manual Lorry test automatically upgrades the bus Pass to a Manual and Vice Versa.
It is true that it doesn’t matter what order you take the tests - you are still entitled to the upgrades, though DVLA may miss them off your licence and you may have to complain to get them added.
What you write is almost a correct statement of the law, which is actually rather more complex. In particular, a manual D test will not upgrade automatic-only CE, but will upgrade automatic-only C.
The full details are in this post - a reply I wrote to you when DVLA screwed up your licence.
The original poster seems to be asking about DE. You are entitled to DE if you pass CE and D tests - it does not matter which order you take the tests in.