Hi! We have not yet switched our curriculum to OG2019—so these problems are not in Navigator and we do not yet have problem sets, etc, set up.
Also: we aren't planning to do this until 2019. On the quant side, the 2019 edition removed questions at all difficulty levels but the replacement questions were mostly of easier-to-medium difficulty. (In other words, the average difficulty of Q questions declined somewhat.) As such, we don't see a huge reason to switch the curriculum at the moment—we'd rather stick with OG2018 for now.
If you've already bought OG19, I don't think you need to go buy OG18—the difficulty level change was not that severe. It just isn't worth switching, if you already have OG18 (like we do).
Our Student Services department does have "conversion lists" (lists that show the OG19 --> OG18 equivalent problem numbers for the ones that stayed). You can send an email to
gmat@manhattanprep.com to ask for the PDF OG conversion lists for Q and V. (Note: we only offer this for the big OG. We don't have it for the two supplemental books, Q-only and V-only.)