There are actually two questions here.
First, why are sections not in order? You have 28 USC §1 through §6, which talk about the Supreme Court, then you have §41 to §49 (appeals courts), then §81 to §144 (district courts) immediately afterwards.
Why is this? Does Congress do this sort of thing to emphasize the "separation" between the types of definitions, or is it just the case that they're "reserving" numbers in case they need to add something (like §40 before §41)? Other examples of this:
- 17 USC §101 through §122, followed immediately by §201 to §205;
- 22 USC § 1 through §136, followed immediately by §141 to §183;
- 18 USC § 2381 through § 2391, followed immediately by § 2421 to § 2429.
- 51 USC § 10101 followed by § 20101, "implying" they skipped 10,100 sections (except they didn't).
Second, why do certain portions of the US Code look like, well, these oddly listed names? Did Congress just run out of numbers or were they trying to "squeeze an entirely new section" in but couldn't quite make it?
- 16 USC §470x-6, § 470aaa, § 590z-11, §668ss
- 15 USC §77bbbb, 79z-6, 80b-21
- 22 USC §2799aa-2
- 42 USC §300mm-62, 1397mm, 2000aa-5, 2000bb-4, 2000gg-6
To me the US Code looks like, well, spaghetti code. And I know lawyers are the ones who look at it and I think they probably couldn't care less about how it looks as long as the law is there, but I'm just curious as to why they opted for the approach of sticking random letters on some of the numbers.