When there are extra tracks on my album compared to the match, Roon gives the ability to add them by filling in the relevant details in the column on the left - this includes disc number and track number.
However, if I tag them on at the end, for example give them track numbers 16 and 17, when I click save and return to the album screen, Roon sets them both as track 1, so that I have 3 track 1’s!