Anecdotally, I've had to think about this in the past with my '82 CB650. When I rebuilt the forks several years ago, I found that there were no back-up plates between the seals and circlips, even though the parts diagrams all show them. I ordered new Honda seals (37x50x11), drove them in, and installed the circlips. Seemed that it would have been nigh impossible to fit anything between.
My guess is that there were later revisions that may or may not have been documented. Maybe thicker seals were used after the diagrams were drawn out and FSMs were written, leaving unrevised documents as the source of truth. I very well might be talking out of my ass though.
But if you are seeing a gap between the seal and the circlip, I suppose you'll need to either source the correct back-up plate or a thicker seal that will fill that gap. Leaky seals are real jerks.
