So acording to the timeline, DeLuca enters his residency in July of 2016. In season 16 he must be in his third year of residency (Season 16 starts in March-April of 2019 aprox).
In Back in the Saddle, Levi says that Tom Koracick's protege is in his fifth year of residency. And when Bailey ask for the pacient diagnostic both DeLuca and Koracick's protege answer seconds before Qadri, so she says "the're three years ahead of us".
So, this means that DeLuca is also in his fifth year of residency, so Qadri, Parker, Helm and Schmitt are in their second year. Or is just an error, because how is possible that DeLuca could be in his fifth year?