It is one thing to buy a pair of guns NIB and find that they are consecutive, it is an entirely different experience finding something consecutive to a gun you own loose in the wild. The older the gun the greater the rush. Part of the thrill of the hunt I guess. I never thought it was a thing myself until the first time I saw a rifle for sale at a local auction and thought "I think I have the serial number next to this" and thus it started. The CMP has made a business model of auctioning consecutive M-1 rifles, which is kind of cool seeing them united from the assembly line 70-80 years ago (although they weren't necessarily produced in consecutive order), which adds another dimension to collecting that rifle, but to find more mundane martial or civilian arms years later that sit numerically next to something you already have in your collection is one of those "Oh WOW!" moments.