Not everyone on fb is on taccoms - just like it to be discussed, if its that reasoning thats its over 10k years old so are many titans etc

Why is there no scope to include a single 'relic' vehicle from 30k? or in this instance the fact that fluff is ignored over preferred models with lower stats? in a normal game? IG shouldnt be limited to only 2 heavy tank variants when countless others used by IG exist

The Falchion was retconned about 20 years ago, it is now a totally different tank. It's not just the main armament, the hull is totally different too. The Mammoth is an even more different tank with a closer resemblance to a giant Spartan assault vehicle.

Fluff wise this is no problem, Falchions were rare 10k years ago, Shadowswords not so much. In the 41st Millenium Shadowswords are rare and Falchions are almost unheard of with the few still existing being treasured relics of the Space Marines. Sufficed to say, to most grunts and even Guard generals, a super heavy tank with an anti Titan weapon is a "Shadowsword" regardless of its actual correct designation.

There's a lot of stuff which has been retconned by GW over the years, so there is a lot of info on Wiki which is not fluff any more, rather just a point of interest for collectors. Generally we go with the most up to date background unless it makes models totally redundant (Squats still exist dammit!). In the case of the Shadowsword/Falchion/Mammoth, as far as Imperial Guard lists, as Army Chapion I'm making the very rare call that we will be going with the "they're different tanks" position as there are totally different models for each these days and most gamers can manage the very straight forward distinction between the two.

Guard already have access to a plethora of super heavy tanks (depending on the list you choose), they don't need the HH Marine ones too (wouldn't marry with the fluff at all or balance particularly well anyway!).