David Weaver
japanese planes because of the hollow, will rely on the condition of the wood just in front of the mouth to work properly.

A double iron wooden plane will show wear in that area fairly quickly, but it will be a long time before it matters because the wood ahead of it and behind it hasn't been removed.

The bearing points on a japanese plane are chosen like that as I believe there wouldn't have been an easy way to true the sole of a plane "superfine" without biasing the process by removing most of the wood. Everything but the toe and the area in front of the mouth is removed so that just those strips can be tuned.

While I may condition a double iron plane once a year or every two years, the literature for japanese planes says that in heavy use, conditioning more than one time in a day was not uncommon.

single iron wooden planes will work OK if the mouth is eroded a little bit as a shaving will be able to lift a little bit, but not unrestricted. The use of the cap iron negates the issue because it works several times better than mouth tightness, and then large parts of the sole need to wear unevenly before truing is necessary.

Just as a follow up comment, I make quite a few planes and so have a long and very flat abrasive lap. It's how I true planes, and it's not historically accurate anywhere. I have trued japanese planes and used them without doing anything else, and they work wonderfully, but my lap is flatter than 99% of table saw tables (there is no area under pressure on it where a 1.2 thousandth feeler will fit under a 24" starrett edge).

I no longer use japanese planes much, but would probably do this in secret for my own use rather than following the traditional method described above. I've modified the wear on a couple to use a double iron more easily and they work great (leading back to the comment above where slight erosion at the mouth becomes a non-issue).