Complex metal loss structures are of distinct concern for pipeline operators, specifically where occurring with significant axial extent. In particular these vital cases often coincide with ILI methodological restrictions. The paper supports the concrete selection of proper ILI techniques by summarizing methodological strengths and limitations of established ILI techniques, like ultrasonic testing, magnetic flux leakage, eddy current, caliper and electromagnetic acoustic transducer. The paper presents the enormous benefit of increased sizing accuracy and unambiguous classification through intelligent combination of multiple data sets. Concrete case examples and details demonstrate the advantages and the background for the sizing improvements. This will include a profound insight to principal techniques, like selective input combination, reliability weighting based on interval overlap, how to correct for systematic errors on the fly or the optimization of river bottom profiles for RSTRENG calculations. Additional to the advantages of simultaneous sizing optimization, case examples will show how to prevent classification traps, overcome data weak points and the reduced need to run similar tools for re-inspections. A principal perspective is opened to significantly increase the ILI sizing accuracy, with selective bypassing methodological obstacles - hurdles often impossible to pass with a standalone technique. Practical recommendations are given to combine proper ILI methods reducing interpretation pitfalls, increasing the data coverage, decreasing the false call rate and improving detection and sizing accuracy.