The method to the numbering seems like a good plan, even if different than what we are used to.
I think the previous point where things became much too random was when they started with anything other than a "1" in the 5th digit. i.e., when 12xxx used to always mean accessory, 11xxx used to mostly mean a set, etc. Once we started with 22xxx, 38xxx, etc (and even some leading with a "1", like 14xxx), it became much more random.
If something is purely identical, it would seem silly to renumber it just for the year. So I'm guessing the bumper example cited above will not result in a 19aabbb number for next years catalog, and then a 20aabbb number if/when cataloged in 2020. (at least I hope not!)
Actually, to the point of a lot (all? I didn't review to check) of the 2018 vol 2 items starting with a 19, that seems wrong to me, but it is what it is. I would have stuck with catalog year vs. intended production year. We all know the actual production schedule can evolve over time, so putting stuff in a catalog called 2018 V2 and starting the numbers with 19 doesn't make any sense at all to me.
So is it a positive or a negative that this scheme only allows Lionel to come up with 1000 unique items in each category for a given year?