I've spent the past few hours doing various tests with bouquets such as with/without main bouquet, multiple providers etc. From what I have gathered, it will be impossible to get "official" numbers across all bouquets if more than one provider is used - this should be pretty self explanatory. For example on Sky UK, BBC One is 101 but on Sky Ireland, 101 is RTE One. So when generating the bouquets, only one of the mentioned channels can get 101. So only your first provider can get "official" numbers.
So the only way you can achieve the "official" numbering effect is if you have one provider and you have a main channel bouquet ("All Channels"). Note that I used the word "effect". This is because a channel in two seperate bouquets cannot have the same number. For example you cannot have "101 - BBC One" in "All Channels" and "101 - BBC One" in "Entertainment". The reason for this is, suppose you are viewing a channel thats in two bouquets, we need to know what bouquet that channel is referencing. 101 cannot be referencing "All Channels" as well as "Entertainment". It has to be one or the other.
So in conclusion, if you have one provider and a main channel bouquet, then it will be possible to achieve the effect of having consistent numbers across different bouquets. However, this will mean that a channel can still be selected using both the "official" number as well the original number in the relevant bouquet. But if the original number is never shown to the user, then it will become very unlikely anyone will remember or even zap the original number. The only way to prevent the user from zapping an original number is to just search a channel number in the main bouquet. But then this will make the whole idea of bouquets pointless as you will only ever be in the main bouquet, unless your only purpose for bouquets is to organise channels into sections in the EPG.
Another alternative in the G-EPG screen is to replace the bouquets with the markers from the main bouquet. By doing this, there will only be one bouquet, but many different sections (similar to what you are used to on Sky). So in this way, no matter what section (marker) you are in, you will still be in the main channel bouquet so there will always be consistent channel numbers. So for this, you just need to generate the main bouquet and not any of the section ones.
Sorry for the long post, I felt it was important to let people know what is possible from a technical point of view. As mentioned above, lets make a seperate thread for this.