Thanks a lot for your answer
After changing your name details on the projects, you should update every project on every computer.
This had been done already, except as I said on the two projects where I can't do anything now since they don't have anymore project page, or the project is down : should I completely detach from these projects ?
Check also that you haven't got multiple records for any computers on any projects. If you have, merge the duplicate records. After doing this it's also necessary to click Update for every project on every computer.
I never see more computers than the 5 computers that I'm currently using on any of the projects I'm crunching for.
The only strange thing (not bothering me much, though) is that since I had to "install" boinc on the other 3 office PC I run by duplicating my whole \boinc directory from my first office PC (no install rights / no write rights on most directory on the 3 other ones), it took some time for the project stats to show each machine with proper stat (ie proper computer ID), and at the end there was a switch between my computer and one of the others : the stat history I ran on my own is now affected to one of the other (much more points, I've been boincing a lot more on my own). But again, it's not a big deal.
Make sure that on each computer you have at least one project that's also on another of your computers. Preferably at least one project that's on every computer you have.
I have 4 projects where all 5 computers can be seen on project pages, 2 where I don't have my own iMac since there is no mac OS X client for them (ABC and malaria) and one that's only on my iMac since I can't make it work on the 4 PC I use at the office (WCG is using https for all communications with project I could never make it work here).
Then wait a day. Update all your projects again. After another day your records should be correct.
I have updated all this several times. For all the 7 projects that I can check, the Cross-project ID is 0f427369fc065729f2235f772e83f26f, same user ID, same email, all seems coherent...
Thanks again for your help.