Keep in mind that of the East Coast long-distance routes, the only ones that go back all the way to 5/1/1971 are the Cardinal (originally George Washington/James Whitcomb Riley) and the Silver services. The rest were added later and so do not have numbers assigned in the Amtrak's original 1971 numbering scheme (LSL as an added route in 1975, Crescent due to Southern not joining Amtrak until 1979, CL as a separate train not combined with the now discontinued Broadway Limited in 1986).
Perhaps in 1986, someone at Amtrak HQ said "while 30-31 makes sense for the CL given their past use on the National Limited and the Broadway being 40-41, it also makes sense to not skip numbers and since 27-28 is used for the PDX section of the Empire Builder, let's continue with the next pair which is 29-30."
Having worked for an airline, I learned early on not to try to make sense of flight numbers. While there were a few patterns, the need to squeeze more and more into a limited space threw much of that out the window. Much of the four-digit range we had (0 to 9999) was reserved with blocks set aside for things like extra sections (no, they didn't fly white flags out the flight deck windows), maintenance flights, code share flights, commuter/express partner flights, etc.). Some numbers were off-limits (anything ending in 13, 13xx (but we didn't waste them - they were used for fake flights for training of reservations and customer service personnel), as well as numbers involved in major incidents in the past). You also preferred not to have similar numbers scheduled to arrive or depart an airport around the same time (both can cause ATC confusion and the latter can cause customer confusion). So sometimes, it was just a matter of what's an available number.
Perhaps in 1986, someone at Amtrak HQ said "while 30-31 makes sense for the CL given their past use on the National Limited and the Broadway being 40-41, it also makes sense to not skip numbers and since 27-28 is used for the PDX section of the Empire Builder, let's continue with the next pair which is 29-30."
Having worked for an airline, I learned early on not to try to make sense of flight numbers. While there were a few patterns, the need to squeeze more and more into a limited space threw much of that out the window. Much of the four-digit range we had (0 to 9999) was reserved with blocks set aside for things like extra sections (no, they didn't fly white flags out the flight deck windows), maintenance flights, code share flights, commuter/express partner flights, etc.). Some numbers were off-limits (anything ending in 13, 13xx (but we didn't waste them - they were used for fake flights for training of reservations and customer service personnel), as well as numbers involved in major incidents in the past). You also preferred not to have similar numbers scheduled to arrive or depart an airport around the same time (both can cause ATC confusion and the latter can cause customer confusion). So sometimes, it was just a matter of what's an available number.