It generally depends on what the designers request in their TOU. Credit is almost always a good idea, but if the designer says it's fine not to in their TOU, then you don't have to. Readers probably would like to know where you got the various parts from, in case they'd like to go find that kit too.
If it's representative of a kit, if you use mostly the same kit for the whole layout, it's definitely nice to mention who made it. If it's a lot of bits and bobs I think it becomes less important.
It generally depends on what the designers request in their TOU. Credit is almost always a good idea, but if the designer says it's fine not to in their TOU, then you don't have to. Readers probably would like to know where you got the various parts from, in case they'd like to go find that kit too.
If it's representative of a kit, if you use mostly the same kit for the whole layout, it's definitely nice to mention who made it. If it's a lot of bits and bobs I think it becomes less important.