Last night I saw a Scout G-1 rocket body part called 1986-088B (according to COSPAR) with my binoculars. I researched a little and found that these rockets had 4 stages, called Algol, Castor, Antares and Altair. I normally assume that is the last stage that remains in orbit with the satellite for any rocket but with so many stages I was wondering if this was the case. How many of these stages remain in orbit? And what stage probably is the 1986-088B object?
In this case, we can be pretty sure it's the last stage.
Objects from the same launch are COSPAR-catalogued with the same number and different letter suffices. 1986-088B is the Scout rocket body, in a 961km x 1015km orbit. 1986-088A is a satellite called Polar Bear that's orbiting at 961km x 1017km -- essentially the same orbit.
Almost all satellites separate from their final booster stages (so as not to have to throw around a lot of dead weight when doing attitude adjustments, and so on), so 088B must be the last stage that contributed significant ∆v to the mission.
If the third stage would remain in (a low) orbit, you would not need a fourth stage. The Scout G-1 was used for low orbits.
Only for high payload orbits both the third and fourth stage could remain in orbits, the fourth stage higher than the third.
The orbit of 1986-088B is fairly high (Min Altitude 961.2 km Mean Altitude 988.3 km Peak Altitude 1015.5 km), that is the reason for its very long existence for 34 years. A third stage remaining in a much lower orbit would have reentered long ago.