How do you sharpen a tongue knife without making the tongue thicker, and how do you sharpen a groove knife without making the groove thinner?
(Architectural Woodworking Forum)
From contributor R:
Face ground will keep everything right providing they did not use side clearance. If the T&G was designed for a back grinding, then there should have been at least 3 degree draft angle so your problem would not exist. You can't have 90 degree in your knives unless you're face grinding or insert tooling which will be thrown away. You could offset the groove knife a bit to make your groove bigger for a quick fix.
The last option would be to opt for a loose fitting T&G when you order your knives. That way as you sharpen the knives, the slight changes in the T&G will still fit together. This style is used a lot in things like flooring and paneling.
One thing to consider, though, if you are sharpening your knives frequently and trying to maintain a tight conventional T&G, you are better off switching to a six-piece carbide tipped cutter set. These sets last far longer than HSS and, if designed right, are adjustable for sharpenings.