After reading the question Where is Vela 1A? Is there any information what its orbit would be like now? and the answer there, it looks like they were deployed in roughly 5 day, 100,000 km circular orbits, which tended to grow quadratically/exponentially(?) in eccentricity over years, then later more slowly in inclination, and now have become quite scattered.
I've plotted all twelve of the Vela spacecraft below. They are called either Vela 1 though Vela 12, or Vela 1A through Vela 6B (launched in pairs).
While of course orbital mechanics is complicated and the effects of the Earth's shape as well as that of the Sun and Moon depend on the details of each orbit, are there any basic principles here that can be understood from this collective plot?
If not, I can make more complicated plots, but I don't want to get into that unless its necessary.
Yes, there are real multi-decade gaps in the TLE histories for these objects. That's what makes it more intriguing!
1963-039A 00674 * VELA 2 1963-039C 00692 * VELA 1 1964-040A 00836 * OPS 3662 (VELA 3) 1964-040B 00837 * OPS 3674 (VELA 4) 1965-058A 01458 * OPS 6577 (VELA 5) 1965-058B 01459 * OPS 6564 (VELA 6) 1967-040A 02765 * OPS 6638 (VELA 7) 1967-040B 02766 * OPS 6679 (VELA 8) 1969-046D 03954 * OPS 6909 (VELA 9) 1969-046E 03955 * OPS 6911 (VELA 10) 1970-027A 04366 * OPS 7044 (VELA 12) 1970-027B 04368 * OPS 7033 (VELA 11)