Why were some WP users not migrated to PHPBB?

[benw]

After migration, do you remember which field your plugin uses to synchronise the users between WP and phpBB ?

Is it only the username, or the email, or both?

After migrating a user from WP, it might be a good idea to store the phpBB user ID in the WP usermeta table (if the plugin doesn't already do that).

[axew3]

it actually check by email when updating, while check for username and email when user register, and if one found the same (even if in wp they do not exists) the registration will be refused, because a query check both for username or email matches in phpBB.

Yes can be a good idea to store phpBB ids into usermeta, by the way since ids will never match, the email is the faster that you can use?
Since the main query, on function verify_phpbb_credentials(){
file /class.wp.w3all-phpbb.php
get user's data by cookie session, so used to check for
if user do not exist in wp, add within
if the user is not logged, login within
if the user need to be updated, update within

unique use of the ID would be when users update profile or login. I assume it would be not so useful, but may i am wrong in some case, i will focus if you have some though about. Email is very fast since it is index, both into phpBB and WP user's DB tables