Yup, although even here you can actually end up failing to see the wood for the trees if you aren't careful.
My current thing is Dogfight Doubles They Never Made But Shoulda. The rules are, one Series 1 and Series 2 kit (or two Series 1 if WW1), and it doesn't matter if either has since been reboxed into a higher series, as long as that tooling was 1 or 2 originally.
To create these, sometimes you can pair two kits with the standard decals, e.g. Hannover CL.III versus DH.4; Hellcat versus Dinah. This is what Airfix usually did, hence anachronisms like the 1940 Bf110 and 1943 JE@J, although in two cases - Cessna/MiG and Mirage/MiG - Airfix provided different decals to make the pair work as a pair (although, as noted above, they still don't).
Often my DFDTNMBS pairs require different decals for one or both aircraft. The Swordfish versus FIAT G50 pairing is fine out of the box, as is the Whirlwind versus Arado 196, but for the Buffalo versus PE2 I need FiAF decals for the Buffalo, while for the Starfighter and HAL Gnat I need PAF and IAF decals.
I also have an F5A versus Jet Provost pair for which I need IRAF and IQAF decals. I spent ages searching online catalogues for the Iranian decals before realising that, er, the kit decals actually are Iranian...OK, IRAF rather than IIAF but I don't think there was a lot of difference.
This is the kind of obvious thing only an obsessive could overlook.