The reason to not allow start weapons to be sold is clearly noted on this board. See them as dull rubbish weapons, they're simply not worth anything. Due to how the game works at the table there's no reason to note weapons as Start, found or bought.
Jafazo wrote:because they didn't buy them from the armory.
Exactly... You forget... I'm UK version. Weapons had no selling to armoury mechanics regardless to being found or bought. It's an extra bonus I've added. It encourages players to try out different plays styles. It's not such a loss if a Dual Wielding Psycho Elf wants to try being a from a far shooter for a while, especially if it wasn't working out after buying that extra sword. Which is super thematic, you're a growing Hero, some ideas aren't going to pan out as well as you thought, highly comical INN topics for the rest of the group.
"Remember that time you thought you were Sir Lightning Foot Slaughters All, yeah you nearly got us all killed! Good thing you found your calling with that Crossbow."
Jafazo wrote:to include notes about where each weapon
No.. Not at all. A start weapon is the start value for that hero and they always default to the start/dull weapon value upon breaking anything bought. For instance, a Barbarian is +1, he has the same rubbish 2 swords as everybody else but gets +1 due to his ferocious strength. It could be said the Dwarf has an AXE but mechanically it doesn't matter, it's the same, a 2. For the Barbarian, this also means he maintains his edge later game once everyone is buffed up. There's often many other hidden reasons to the twists that managed to stay in my Mod Sheet.
A found weapon is noted as they'd have the card (Remember, UK version (edit: actually this is originally the other way round but, we flip it, allowing multiples of the same weapon to be bought and the cards are used as a randomiser for the armoury search)). However, if they tricked a shop keeper into buying it, no real harm, as you wrote "Just roleplay it". If not, they're free to sell it to another player or discard it.
The buy back mechanic is purely introduced as encouragement for Heroes to make side steps, slowing the power creep in progression, trying out new play styles. Technically, as there's no original carry restrictions, with out a buy back, they'd simply own everything (edit: no need to go into debating carry restrictions mods)
I do appreciate your quest for errors in the mods I use, normally people don't look as deeply into it. At least I know it's not getting ignored and it's how new ideas and reasoning can be reached.