The regulation of particle number (PN) has been introduced in the Euro 5/6 light-duty vehicle legislation, as a result of the light duty inter-laboratory exercise of the Particle Measurement Program (PMP). The heavy-duty inter-laboratory exercise investigates whether the same or a similar procedure can be applied to the heavy-duty regulation. In the heavy-duty exercise two "golden" PN systems sample simultaneously; the first from the full dilution tunnel and the second from the partial flow system. One of the targets of the exercise is to compare the PN results from the two systems. In this study we follow a different approach: We use a PMP compliant system at different positions (full flow, partial flow and tailpipe) and we compare its emissions with a "reference" system always sampling from the full flow dilution tunnel. The results from two heavy-duty diesel engines equipped with Diesel Particulate Filters (DPFs) show that full flow and partial flow systems emissions have negligible differences (≺10%), while at the tailpipe lower emissions are measured probably due to thermophoretic losses. The small difference between full flow and partial flow systems remains even for different emission levels (i.e., engine without and with different DPFs). The real-time patterns at all sampling positions show an excellent agreement with the pattern of the reference system connected to the full dilution tunnel. Finally, the presence of non-volatile materials below 23 nm is investigated. The non-volatile particles ≺23 nm generally follow the pattern of the non-volatiles ≻23 nm but depending on the engine and the cycle, they are 70-500% higher.