Well, originally I intended to propose that when the user ticks "Other" an additional field could appear where the user fills in where the game was purchased from, which would in turn replace "Other" with whatever the user wrote, but it kind of seemed like a wild "spitball" so I figured I'd keep it to myself. Just for clarification, in this scenario when the user checks the platform the game is from, the others would disappear, leaving only the one that was chosen when they add the item to their collection. And yes, I'm certain others use the notes field the same as you do, I reckon it's there and it's meant to be used any way we see fit; but if the website were to follow through with what we're discussing, I believe that it should have a concrete way for its users to classify their digital collection just the same way it's done for physical items. Plus, not for nothing, but it's odd for digital releases to keep the same fields physical ones have; and by that I mean, "Cart/Disk/Item", "Case/Box", and "Manual". Sure, some digital games tend to include a manual (PDF), but that's where I think the notes field would come into place, especially when we consider some also include artbooks, soundtracks, and other extras.
Nonetheless, like I said above, I'm just spitballing; I'm sure there are other ways to go about doing this. Like, for example, all four checkboxes could be replaced with a field where users themselves write down where they bought/got the game from; however, there's the probability of it being used improperly. Another possible option is a drop-down list—I'm sure we can come up with more.
