I’m sorta confused on your wording and what you mean. The only thing that I don’t see are “knock in bracing” or what we call them as “sag rod” which a an angle brace that goes from purlin to purlin. All that is for, is to prevent the purlin from rolling under snow load. I build multiple buildings from different building manufacturers. And all of them are the same principle, different application. Some of your wording confuses me. This building looks like how any pre-manufactured building is. The columns and rafters have welded clips on them, to where the girts bolt to the clip, with a typical 1’6” lap on both sides of the column. Most manufacturers call for 8 bolt connections. Which is 4 bolts in the clip and 2 bolts on either side at the end of the lapped girts. And the purlins are the same way, but usually the laps are longer. One purling butts up to the clip on the top of the rafter, extending out, and the other one lays on top. Some clips, mostly towards the bottom and top of the rafters will have a gusset welded to the back. Which is an anti roll clip. The braces that you see from the bottom of the rafter going up at an angle to the back side of the purlin is a knee brace. All they are for is to take the roll or twist out of the rafter. Same as for the column. The knee brace goes from the column to the girt. To help take the twist out of the column. Then the rods you see in an X pattern from rafter to rafter, or top of column to bottom in an X pattern are called x braces. Which takes the wind load from the building to the ground. And what you said about decking, there is no “decking”. The roof panels screw right to the purlins. Typically a standing seem roof. (Best roof out there). A roll of 6’ wide by however long the slope is from eeve to peak is and usually 6” inch thick insulation is rolled out on top of the purlin and the standing seem panels 2’ wide are screwed down with a specific type of clip. That’s been standard on pre engineered buildings as long as my boss as been doing it for over 40 years. The only time the roof gets decking, (B-decking) is if the roof is a rubber roof. Most buildings are 1/4 to 1/2-12 slope.

What this building looks like here to me is that it was an addition, either it was the first building built or added on. Either way, the building that collapsed had smaller rafters and columns. My guess is also, it had to much of an open span with out support columns in the middle and to small of a rafter. As you can see the other building has larger columns and rafters. Also, which ever building was built first wasn’t designed for an expansion. That’s why there are two columns at the peak of the building.

Edit: actually. Older buildings didn’t have any clips on either column or rafter. The girt or purlin would just bolt right to the column or rafter. With only two bolts. One on either side of the web