Main Venting Review

I have a 112 year old home with a Burnham boiler and one pipe steam system. The boiler is 30 years old and virtually all of the piping is original and in great shape. I had to replace a leaking wet return a few years ago. My question/concern is: I have two mains, one branches off in two directions and has two Hoffman #75 vents at one end, just above where it drops into a wet return, and two additional Hoffman 75 vents at the other end, about 4 feet before it makes a 90 degree turn and returns to the boiler/wet return.

The second main takes off in another direction and branches off to a leg that has three radiator risers attached to it.It has a dry return on the end of that leg and runs back to a wet return (no venting). The main then makes a loop and ties back into a common return as main #1 but that  connection is 5 feet down stream (closer to the boiler than the vents at that end of main #1. This all looks like the original setup (except for the Hoffman vents which I replaced and added another one at each end). I have been over the second loop with a fine tooth comb and see no indication that there was ever a vent on that loop.The system is very quiet, runs great, radiators all get hot within a minute or two of each other and I'm running at between .5psi to 1psi except on really cold days (zero or below)when my boiler may cut out on pressure a couple times.

Have any of the pros on this site seen this type layout and should I be concerned about adding vents to the second main or is it actually pushing air out of the vents on Main #1 near the common return to the boiler? I know they say "If its not broke, don't fix it" but if I can get a little more efficient, maybe I should try. I have a diagram of the layout but I don't know how to post it??