I was helping a neighbor hang some T1-11 this weekend and we ran into an
issue I didn't expect. It's been a long time since I hung T1-11 but I don't
recall having this problem last time.

We installed 6 sheets, which meant that there was 5 vertical seams. 3 of
the sheets slid right into place with the ship-lap over lapping perfectly,
leaving a vertical groove that matched the grooves in the field and faces
that were flush. However, 2 of the sheets wouldn't slide over far enough,
resulting in a larger groove at the seam.

When we looked at the back side of the first sheet that gave us a problem,
we found that there was extra wood, almost like a tongue, in the area where
the sheet should have overlapped the sheet to the left of it. That wood was
hitting the edge of installed sheet, preventing it from sliding as far as
it should have. I grabbed my circular saw, set it for the depth of the
"lap" and trimmed off the extra wood. It then slid perfectly into place. We
found one other sheet that had the same "tongue" and, as suspected, it
wouldn't slide over far enough either, so we trimmed that one also, giving
us a perfect fit.

Has anyone else run into this issue? Was the extra wood just poor quality
manufacturing? Is it fairly common?