I agree to split the issues and treat data and modelling separately.
Data: While it is true that the incineration of average MSW "produces" aluminium, iron and copper scraps, the incineration of biowaste does not. 1 kg of Carrots supplied by the global market comes with 120 grams of biowaste, which is treated in the RoW and CH markets of biowaste treatment. A share of this treatment is done by incineration, but without "producing" aluminium scrap. Hence, carrots must find other ways to enter the MSW route and thus the aluminium alloy production. One of them might be the route of treatment of biowaste by composting, during which 18.5 mg of MSW is generated per kg of biowaste.
Modelling: the usual way of optimising waste treatment and recycling chains is by direct allocation of the various valuable products of the waste treatment activity (e.g. biowaste incineration: allocation between the three products waste treatment service, electricity and heat; biowaste anaerobic digestion: allocation between the three products waste treatment service, biogas and compost).
In case studies (not in background databases) about the environmentally preferable waste treatment options, one may also apply the basket of benefit or the avoided burden approaches.
I do not yet see the point of allocating a share of vegetables production to aluminium recycling as a means to optimise waste treatment chains (in the global vegetables and fruits (carrots, apples etc.) markets as represented in ecoinvent). And I do not see the message to convey with the fact that aluminium recycling requires efforts and causes emissions in vegetables and fruits production. Should aluminium recyclers plea for organic vegetables production to lower their recycled metals' footprints?
Data in database: Many important recycling activities are present in the ecoinvent data v2 such as metals recycling, anaerobic digestion, electronic waste treatment. Some recycling processes are missing like plastics recycling. Processes using secondary fuels such as clinker (cement) production and processes where energy is recovered such as waste incineration rpocesses are present too. Hence, many of these activity datasets are present, some links to and from them are (intentionally) not.
Best regards, Rolf