I'm going on second hand info from some friends in my dojo who have trained at the hombu a year or so ago, so this may not be 100% accurate but anyhow,
They (at the hombu) seem to be a little fussy about name dropping to let you train. To give the example that happened to my friends: They arrived with membership books (to our organisation) showing grades etc and a letter of recommendation from a high ranking sensei. We had just got new (member) books as the old ones were falling to pieces. The problem was that the new books didn't have the technical director of our organisation named on them. (Tamura Sensei)
It was looking as if they were going to be unable to train
until one of my friends found that he'd brought his old book with him, stating the linkage to the Aikikai.
Moral of the story? Take something which the Japanese will recognise and be able to verify. I've no idea if this was a one off occurrence but if in doubt always be preparedů
Hope this helps