Confusion about the model file

Dear colleagues: I am confused about the compartments of model files. Does the NBOLUS1 compartment not exist? Is the RATEIV(1) the central compartment? Take the figure below as an example. An oral drug is administered into the NBOLUS1 compartment, and then is absorbed into the RATEIV(1)（ the central compartment). So the model file does not have the peripheral compartment. It is, actually, a one-compartment model for oral drugs. If I want to construct a model of imatinib, but I only have trough concentrations, should I choose the one-compartment model, which only has RATEIV(1) compartment? I look forward to hearing back from you! Kind regards!