Why did we need to trim T1-11 to get it to fit?

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?
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I assume you mean that we should check the edges of ship-lap products also.
T1-11, as far as I know, is always ship-lap, not T&G. I could be wrong, but if I'm not, then any "tongue" on the edge of T1-11 is nothing more than bad manufacturing.
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Yes, that is T1-11 but that's not T&G .
Look at the first three products at this site. The first two are T&G, the third is ship-lap.
http://www.kellyfradet.com/home-exterior/siding-trim-and-millwork/wood-t-g-and-clapboard
As far as I know, all T1-11 is ship-lap.
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On Monday, September 16, 2013 1:40:23 PM UTC-5, DerbyDad03 wrote:

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 t hat 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 shee ts 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 whe re 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 woul dn'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?
Yes, it was poor quality manufacturing and poor quality inspection of the f inished product. As others have said, it is not uncommon.
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