Hello Peter and All,
Most of my excluders are fairly recent manufacture and from Dadant, Kelley and Mann Lake and I have no problem with bees passing through regardless of the foundation used. 

I first became aware of the problem of excluder spacing on old excluders was after we bought out a Mennonite beekeeper which had equipment  which was old and had not been in service for over fifteen years.

 Myself and two other beekeepers purchased the equipment.
I tossed my share of the queen excluders in the shed. One of the beekeepers put his in service right away. He called me later in the week to come look at his bees.  
I found workers dead  and  dying bees stuck in the slots of the shiny excluders.

He pulled the     excluders (about a hundred) and put on newer excluders and the problem was solved.

The bees were  from the Walter Kelley company. Kelley was producing foundation in the 5.3mm range then so maybe the bees were a bit larger than the norm. The bees were on 5.3mm wired Kelley foundation.

The only logical conclusion we could come to was that these old excluders had a narrower spacing. We did not measure either the old excluders or the new excluders BUT the newer excluders solved the beekeepers problem. . Maybe I will measure when I get caught up around here. I have no idea of the maker of those old excluders .
Sincerely,
Bob Harrison 

Ps. Most of the old excluders had last been in service in the late 70's  but some had not ever been in service. Again I have not a clue to the manufacturer or the year of manufacture